Cellulose acylate film, optically compensatory film, polarizing plate and liquid crystal display

ABSTRACT

A cellulose acylate film is provided and contains an additive. Tg of the cellulose acylate film is lower by 5 to 50° C. or the half value width of the diffraction peak at 2θ=10 to 15° in the X-ray diffraction pattern of the cellulose acylate film after heating at 200° C. for 3 hours is 110 to 300%, each compared with a cellulose acylate film not containing the additive. An optically compensatory film, and a polarizing plate and a liquid crystal display using the film are provided.

TECHNICAL FIELD

The invention relates to a cellulose acylate film useful in liquidcrystal displays and, moreover, to optical materials such as anoptically compensatory film and a polarizing plate and a liquid crystaldisplay using the same.

BACKGROUND ART

Because of being excellent in transparency and free from opticaldefects, cellulose acylate films have been employed as protective filmsfor polarizing plate which is one of members constituting a liquidcrystal display. In general, a polarizing plate is obtained by dyeing astretched polyvinyl alcohol (PVA)-based film with iodine or a dichroicdye to give a polarizer and stacking a protective film on at least oneside thereof. Cellulose acylate films, in particular, triacetylcellulose acylate films which can be stacked directly on PVA areemployed in may cases.

Since the characteristics of a liquid crystal display largely depend onthe optical characteristics of a protective film of a polarizer,requirement for the improvement in the qualities thereof is growing yearby year. In liquid crystal displays in these days, it is more stronglyrequired to improve the display performance in looking from an angle,i.e., the viewing angle characteristics. To improve the viewing anglecharacteristics, it is important to have an appropriate retardationvalue represented by the product of the birefringence and thickness of aprotective film of a polarizing plate and another optical film employed.It has been a practice to employ an optically compensatory film for thispurpose.

In order to control the retardation value by using an opticallycompensatory film, it is desirable to minimize the retardation value ofa protective film with avoiding excess. In a protective film, it isparticularly advantageous for improving the viewing angle-dependency tolower not only the in-plane retardation value (Re) but also thethickness direction retardation value (Rth).

Although there have been produced cellulose acylate films having a smallin-plane retardation Re, a cellulose acylate film having a small Rth canbe hardly produced. In recent years, there have been proposed opticallytransparent films having small thickness direction retardation value Rthwith the use of a polycarbonate-based film or a thermoplasticcycloolefin film (see, for example, JP-A-2001-318233 andJP-A-2001-328233; examples of commercially available products beingZEONOR (manufactured by ZEON CORPORATION) and ARTON (manufactured byJSR)). These films are characterized by being advantageous in showingsmall dimensional change and low vapor transmission rate. In the case ofusing as a protective film of a polarizer, however, these opticallytransparent films suffer from a problem that they cannot be directlystacked on hydrophilic PVA because of the hydrophobic nature thereof.Moreover, there still remains another problem that the opticalcharacteristics in the entire film face are uneven.

Furthermore, these polycarbonate-based films and cycloolefin-based filmslargely differ in physical properties from cellulose acylate filmshaving been employed as protective films of polarizing plates hitherto,which bring about another industrial disadvantage that the existingequipment for manufacturing polarizing plates should be renewed.

On the other hand, it is required to improve the physical stability ofcellulose acylate films and, therefore, the dimensional change and vaportransmission rate should be lowered.

DISCLOSURE OF THE INVENTION

An object of an illustrative, non-limiting embodiment of the inventionis to provide a cellulose acylate film which has small Re and Rth and isexcellent in physical characteristics, in particular, showing a smalldimensional change. Another object of an illustrative, non-limitingembodiment of the invention is to construct a protective film of apolarizing plate or an optically compensatory film being excellent inviewing angle characteristics and provide a liquid crystal display withthe use of the same.

By adding a compound in a controlled amount to cellulose acylate, theinventors regulated the glass transition temperature (Tg) of a film to alevel lower by 5 to 50° C. than the glass transition temperature of afilm not containing the above compound. By elevating the half valuewidth of the X-ray diffraction peak of the former film to 110 to 300% ofthe half value width of the film not containing the compound,appropriate crystallization was achieved within the film. Owing to thesefactors, the physical characteristics (dimensional change, modulus ofelasticity, vapor transmission rate, etc.) of the cellulose acylate filmof the invention could be improved compared with the film not containingthe additive. By employing an additive by which the physicalcharacteristics of the film can be improved and Re and Rth can belowered, a cellulose acylate film having practically usable physicalcharacteristics and optical characteristics favorable in using in liquidcrystal displays and so on could be successfully produced.

The invention has been completed based on the following <1> to <28>.

<1> A cellulose acylate film comprising an additive, the celluloseacylate film fulfilling at least one of requirements (1) and (2):

(1) the cellulose acylate film has a glass transition temperature lowerby 5 to 50° C. than that of a cellulose acylate film not containing theadditive; and

(2) the cellulose acylate film having been heated at 200° C. for 3 hourshas a half value width of a diffraction peak at 20 of 10 to 15° in anX-ray diffraction pattern thereof, the half value width being 110 to300% of a half value width of a cellulose acylate film not containingthe additive and having been heated at 200° C. for 3 hours, and (3) thecellulose acylate film further fulfilling numerical formulae (1) and(2).

0≦Re ₆₃₀≦10, and |Rth ₆₃₀|≦25  Numerical formulae (1)

|Re ₄₀₀ −Re ₇₀₀|≦10, and |Rth ₄₀₀ −Rth ₇₀₀|≦35  Numerical formulae (2)

wherein Re(λ) indicates an in-plane retardation (expressed in nm) of thecellulose acylate film at a wavelength of λ (nm); and Rth(λ) indicates athickness-direction retardation (expressed in nm) of the celluloseacylate film at a wavelength of λ (nm).<2> The cellulose acylate film as described in <1>, which has anabsolute value of dimensional change after standing at 60° C. and 90%for 24 hours, the absolute value being 5 to 90% with respect to anabsolute value of dimensional change of a cellulose acylate film notcontaining the additive.<3> The cellulose acylate film as described in <1> or <2>, which has amodulus of elasticity of 101 to 150% with respect to a modulus ofelasticity of a cellulose acylate film not containing the additive.<4> The cellulose acylate film as described in any one of <1> to <3>,which has a photoelasticity of 105 to 150% with respect to aphotoelasticity of a cellulose acylate film not containing the additive.<5> The cellulose acylate film as described in any one of <1> to <4>,which has a density of 99.9% or less with respect to a density of acellulose acylate film not containing the additive.<6> The cellulose acylate film as described in any one of <1> to <5>,which has a vapor transmission rate of 30 to 90% with respect to a vaportransmission rate of a cellulose acylate film not containing theadditive.<7> The cellulose acylate film as described in any one of <1> to <6>,which has a contact angle after alkali saponification of 95% or lesswith respect to a contact angle after alkali saponification of acellulose acylate film not containing the additive.<8> The cellulose acylate film as described in any one of <1> to <7>,which has a tear strength of 95% or less with respect to a tear strengthof the cellulose acylate film not containing the additive.<9> The cellulose acylate film as described in any one of <1> to <8>,which has a coefficient of humidity expansion of 95% or less withrespect to a coefficient of humidity expansion of a cellulose acylatefilm not containing the additive.

<10> The cellulose acylate film as described in any one of <1> to <9>,which is obtained from a starting polymer having an acylation ratio of2.85 to 3.00.

<11> The cellulose acylate film as described in any one of <1> to <10>,wherein the additive is a compound capable of lowering Rth_(λ) in such arange as fulfilling the following numerical formulae (3) and (4):

(Rth _(λA) −Rth _(λ0))/A≦<−1.0  Numerical formula (3)

0.01≦A≦30  Numerical formula (4)

wherein Rth_(λA) indicates Rth_(λ) (nm) of a cellulose acylate filmcontaining A % by mass (weight) of the compound capable of loweringRth_(λ); Rth₀ indicates Rth_(λ) (nm) of a cellulose acylate film notcontaining the compound capable of lowering Rth_(λ); and A indicates anamount of the compound capable of lowering Rth_(λ) expressed in mass (%)referring the mass of the polymer material of the cellulose acylate filmas to 100.<12> The cellulose acylate film as described in <11>, wherein thecompound capable of lowering Rth_(λ) has an octanol-water partitioncoefficient (log P value) of 0 to 7.<13> The cellulose acylate film as described in <11> or <12>, whereinthe compound capable of lowering Rth_(λ) is a compound represented byformula (1) or (2):

wherein R¹¹ represents an alkyl group or an aryl group; R¹² and R¹³ eachindependently represents a hydrogen atom, an alkyl group or an arylgroup; R²¹ represents an alkyl group or an aryl group; and R²² and R²³each independently represents a hydrogen atom, an alkyl group or an arylgroup.<14> The cellulose acylate film as described in any one of <1> to <13>,wherein the additive is a compound capable of lowering |Re₄₀₀−Re₇₀₀ |and |Rth₄₀₀-400−Rth₇₀₀| in an amount of 0.01 to 30% by mass based on asolid content of a starting polymer of the cellulose acylate film.<15> The cellulose acylate film as described in any one of <1> to <14>,which has a spectral transmittance at the wavelength of 380 nm of 45 to95% and a spectral transmittance at the wavelength of 350 of 10% orless.<16> The cellulose acylate film as described in any one of <1> to <15>,which has a film thickness of 10 to 120 μm.<17> A method of producing a cellulose acylate film as described in anyone of <1> to<16>, which comprises: casting a cellulose acylate solution on a supportto provide a film; stripping off the film from the support; and dryingthe film, wherein the amount of the solvent remaining in the film at thestripping is 50 to 200%.<18> A method of producing a cellulose acylate film as described in anyone of <1> to <16>, which comprises: casting a cellulose acylatesolution on a support to provide a film; stripping off the film from thesupport; and drying the film at a temperature of 120 to 160° C.<19> An optically compensatory film comprising: a cellulose acylate filmas described in any one of <1> to <16>; and an optically anisotropiclayer having Re₆₃₀ of 0 to 200 nm and |Rth₆₃₀| of 0 to 400 nm.<20> The optically compensatory film as described in <19>, wherein theoptically anisotropic layer contains a discotic liquid crystal layer.<21> The optically compensatory film as described in <19> or <20>,wherein the optically anisotropic layer contains a rod-shaped liquidcrystal layer.<22> The optically compensatory film as described in any one of <19> to<21>, wherein the optically anisotropic layer contains a polymer film.<23> The optically compensatory film ac described in <22>, wherein thepolymer film constituting the optically anisotropic layer contains atleast one polymer material selected from the group consisting ofpolyamide, polyimide, polyester, polyetherketone, polyamidimde,polyesterimide and polyaryl-ether ketone.<24> A polarizing plate comprising: a polarizer; and a protective filmbeing at least one cellulose acylate film as described in any one of [1]to [16] or an optically compensatory film as described in any one of[19] to [23].<25> The polarizing plate as described in <24>, which has at least onelayer on a surface thereof, the at least one layer being selected formthe group consisting of a hard coat layer, an antiglare layer and anantireflection layer.<26> A liquid crystal display comprising a cellulose acylate film asdescribed in any one of <1> to <16>, a optically compensatory film asdescribed in any one of <19> to <23> or a polarizing plate as describedin <24> or <25>.<27> The liquid crystal display as described in <26>, which is a VAliquid crystal display or an IPS liquid crystal display.<28> The liquid crystal display as described in [27], which is an IPSliquid crystal display, wherein the liquid crystal display comprises aliquid crystal cell; two polarizing plates, one of the two pnolarizingplate being in the top side of the liquid crystal, the other of the twopolarizing plate in the bottom side of the liquid crystal cell, and atleast one of the two polarizing plates having a cellulose acylate filmas described in any one of <1> to <16>.

Use of a cellulose acylate film of the invention, which has improvedphysical properties such as film dimensional change, modulus ofelasticity and vapor transmission rate and lowered Re and Rth, makes itpossible to construct a protective film of a polarizing plate or anoptically compensatory film having excellent viewing anglecharacteristics. Moreover, it is effective to employ a cellulose acylatefilm of the invention in an IPS mode liquid crystal display, since colorchange in looking from an angle can be lessened and light leakage in theblack display can be relieved thereby. In the case of using a celluloseacylate film of the invention in a VA mode liquid crystal display, thecontrast viewing angle characteristics in looking from an angle can beimproved.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic view showing an IPS mode liquid crystal displayprovided with an exemplary cellulose acylate film of the invention.

DETAILED DESCRIPTION OF THE INVENTION Best Mode for Carrying Out theInvention

Exemplary embodiments of the invention will be illustrated in greaterdetail.

<Cellulose Acylate Film>

As mentioned above in <1>, a cellulose acylate film of the invention isa cellulose acylate film containing an additive which is characterizedby satisfying at least one of the two requirements (1) and (2) and alsosatisfying the requirement (3).

The requirement (1) in the above <1> is a cellulose acylate filmcontaining an additive wherein the glass transition temperature(hereinafter referred to as Tg) of the cellulose acylate film is lowerby 5 to 50° C. than Tg of a cellulose acylate film not containing theadditive. It is preferable that the former Tg is lower by 10 to 50° C.,more preferably 15 to 50° C., than the latter Tg.

As the results of intensive studies, the inventor has succeeded inregulating Tg within the range as defined above by selecting anappropriate type of additive and controlling the content of theadditive. In general, Tg is lowered and the film is softened with anincrease in the content of the additive. In the invention, Tg isregulated within the desired range as defined above by avoiding to usethe additive in excess and preventing excessive lowering in Tg. As aresult, the cellulose acylate film of the invention has improvedphysical properties compared with the film before the addition of theadditive.

So long as the lowering in Tg of the cellulose acylate film containingthe additive of the invention is 5° C. or more compared with Tg of thecellulose acylate film not containing the additive, the additive ishighly compatible with cellulose acylate and well dissolved therein,thereby giving a stable dope solution. Owing to the additive containedin an appropriate amount, the film has an adequately hydrophobic natureand thus dimensional change due to change in humidity can be maintainedat a low level. In this case, furthermore, the film is neither too hard,fragile nor easily torn and there arises no problem in the physicalcharacteristics of the film. So long as the lowering is not more than50° C., the film would not suffer from troubles in physicalcharacteristics (for example, worsening in elasticity or worsening inheat resistance). Therefore, it causes no serious worsening inperformance when employed in a liquid crystal display, etc.

In the invention, Tg is defined in accordance with JIS K-7121.

The requirement (2) in the above <1> is a cellulose acylate filmcontaining an additive wherein the half value width of the diffractionpeak at 2θ=10 to 15° in the X-ray diffraction pattern of the celluloseacylate film, which has been heated at 200° C. for 3 hours, is 110 to300% of the half value width of the cellulose acylate film notcontaining the additive which has been heated at 200° C. for 3 hours. Itis preferable that the former half value width is 110 to 250%, morepreferably 110 to 200%, of the latter half value width. This factindicates that, when the diffraction peak of the cellulose acylate filmcontaining the additive of the invention is compared with thediffraction peak of the cellulose acylate film not containing theadditive, the diffraction peak is elevated. This means that, in thecellulose acylate film containing the additive of the invention, theregularly repeated structure forming the diffraction peak is remarkablecompared with the cellulose acylate film not containing the additive.

So long as the half value width of the diffraction peak at 2θ=10 to 15°in the X-ray diffraction pattern of the cellulose acylate film fallswithin the range as defined above compared with the half value width ofthe cellulose acylate film not containing the additive which has beenheated at 200° C. for 3 hours, the film contains a repeated regularstructure forming the diffraction peak at an appropriate level and thusthe physical characteristics (for example, dimensional change, modulusof elasticity, vapor transmission rate and so on) can be improved.

The requirement (3) in the above <1> is a cellulose acylate filmcontaining an additive and the optical performance of the film fulfillsthe following numerical formulae (1) and (2):

0≦Re ₆₃₀≦10, and |Rth ₆₃₀|≦25  Numerical formulae (1)

|Re ₄₀₀ −Re ₇₀₀|≦10, and |Rth ₄₀₀ −Rth ₇₀₀|≦35  Numerical formulae (2)

In the above formulae, Re₆₃₀, Re₄₀₀ and Re₇₀₀ indicate the in-planeretardations (expressed in nm) of the cellulose acylate film atwavelength of 630 nm, 400 nm and 700 nm respectively; and Rth₆₃₀, Rth₄₀₀and Rth₇₀₀ indicate thickness-direction retardations (expressed in nm)of the cellulose acylate film at wavelength of 630 nm, 400 nm and 700 nmrespectively.

To improve the viewing angle dependency in a liquid crystal display, itis preferable that the optical performance of the cellulose acylate filmcontaining the additive fulfills the following numerical formulae (1′)and (2′), more preferably (1″) and (2″).

0≦Re₆₃₀≦8, and |Rth ₆₃₀≦23;  Numerical formula (1′)

|Re ₄₀₀ −Re ₇₀₀|≦8, and |Rth ₄₀₀ −Rth ₇₀₀|≦30.  Numerical formula (2′)

0≦Re₆₃₀≦5, and |Rth ₆₃₀|≦30;  Numerical formula (1″)

|Re ₄₀₀ −Re ₇₀₀|<5, and |Rth ₄₀₀ −Rth ₇₀₀≦25.  Numerical formula (2″)

As discussed above, the cellulose acylate film containing the additiveof the invention should fulfill at least one of (1) and (2), among thethree requirements as described above, to improve the physicalcharacteristics and also fulfill the requirement (3) to improve theviewing angle characteristics.

(Evaluation of the Performance of Cellulose Acylate Film) (Measurementof Retardation) (In-Plane Retardation Re and Thickness-DirectionRetardation Rth)

After conditioning a sample (30 mm×40 mm) at 25° C. and 60% RH for 2hours, Re? is measured by the incidence of a ray of λ nm in wavelengthin the normal direction with the use of an automatic doublerefractometer KOBRA 21 ADH (manufactured by OJI KEISOKU KIKI). Rth_(λ)is calculated based on retardation values including Re_(λ) as describedabove and retardation values measured by the incidence of a ray of λ nmin wavelength in directions inclining to 40° at intervals of 10° to thenormal direction (i.e., 0°) of the film using the slow axis in the planeby inputting a presumptive average refractive index (1.48) and the filmthickness.

(Measurement of Wavelength Dispersion of Re and Rth)

After conditioning a sample (30 mm×40 mm) at 25° C. and 60% RH for 2hours, Re is at each wavelength is measured by the incidence of rays of780 nm to 380 nm in wavelength in the normal direction of the film withthe use of an ellipsometer (M150 manufactured by JASCO ENGINEERING).Thus, the wavelength dispersion of Re is determined. On the other hand,the wavelength dispersion of Rth is determined based on threeretardation values measured in three directions, i.e., the Re asobtained above, a retardation value measured by the incidence of rays of780 to 380 nm in wavelength in a direction inclining at +40° to thenormal direction of the film using the slow axis in the plane as theincline angle and a retardation value measured by the incidence of raysof 780 to 380 nm in wavelength in a direction inclining at −40° to thenormal direction of the film using the slow axis in the plane as theincline angle and inputting a presumptive average refractive index(1.48) and the film thickness.

It is preferable that the absolute value of the dimensional change afterstanding at 60° C. and 90% for 24 hours of the cellulose acylate filmcontaining the additive of the invention is from 5 to 90% of theabsolute value of dimensional change the cellulose acylate film notcontaining the additive. It is still preferable that the former absolutevalue is from 5 to 80%, more preferably from 5 to 70%, of the latter.

The dimensional change is measured in practice by preparing a celluloseacylate film sample (30 mm×120 mm; referring the machine direction (MD)as the long side), conditioning the sample at 25° C. and 60% RH for 24hours, punching holes of 6 mm in diameter at intervals of 100 mm on bothedges of the sample by using an automatic pin gauge (manufactured bySHINTO SCIENCE Co., Ltd.) and referring the intervals among the holes asthe original size (L0). Next, the sample is treated at 60° C. and 90% RHfor 24 hours and the intervals among the holes (L1) are measured. Eachmeasurement is made to the minimum scale value of 1/1000 mm. Afterstanding at 60° C. and 90% RH for 24 hours, the dimensional change rateis determined as follows. Dimensional change rate={|L0−L1|/L0}×100.Subsequently, the ratio of the absolute value of the dimensional changerate of the cellulose acylate film containing the additive to that ofthe cellulose acylate film not containing the additive is calculated.

It is preferable that the modulus of elasticity of the cellulose acylatefilm containing the additive of the invention is from 101 to 150% of themodulus of elasticity of the cellulose acylate film not containing theadditive. It is still preferable that the former modulus of elasticityis from 105 to 140%, more preferably from 110 to 130%, of the latter.The modulus of elasticity is determined in practice by measuring thestress at a 0.5% elongation at a tensile speed of 10%/min in anatmosphere at 23° C. and 70% RH with the use of a multipurpose tensiletest machine STM T50BP (manufactured by TOYO BALDWIN).

So long as the modulus of elasticity of the cellulose acylate filmcontaining the additive falls within the range as defined above based onthe modulus of elasticity of the cellulose acylate film not containingthe additive, the film suffers from no problem in physicalcharacteristics. When it is employed in a liquid crystal display, etc.,moreover, there arises no remarkable worsening in performance.

It is preferable that density of the cellulose acylate film containingthe additive of the invention is not more than 99.9% of the density ofthe cellulose acylate film not containing the additive. The density isdetermined in practice by conditioning the sample at a temperature of25° C. and a humidity of 50% RH for 24 hours and then measuring thedensity thereof in a density gradient tube (n-heptane/carbontetrachloride) at 25° C.

It is preferable that the vapor transmission rate of the celluloseacylate film containing the additive of the invention is from 30 to 90%of the vapor transmission rate of the cellulose acylate film notcontaining the additive. It is still preferable that the former vaportransmission rate is from 30 to 80%, more preferably from 30 to 70%, ofthe latter. It is preferred that the vapor transmission rate of thecellulose acylate film containing the additive is not more than 90% ofthe vapor transmission rate of the cellulose acylate film not containingthe additive, since the Re and Rth values of the film do not vary inthis case. It is preferred that the vapor transmission rate of thecellulose acylate film containing the additive is 30% or more of thevapor transmission rate of the cellulose acylate film not containing theadditive, since no problem (adhesion failure, etc.) occurs in the caseof constructing a polarizing plate by laminating the cellulose acylatefilm of the invention on a polarizer as a protective film of apolarizing plate.

The vapor transmission rate is measured at a temperature of 60° C. and ahumidity of 95% RH in accordance with JIS Z-0208. As a method ofmeasuring the vapor transmission rate, use can be made of a methoddescribed in Kobunshi no Bussei II (Kobunshi Jikken Koza 4, KyoritsuShuppan), p, 285 to 294: Joki Tokaryo no Sokutei(Shisuryo-ho,Ondokei-ho, Jokiatsu-ho, Kyuchaku-ho). A sample (70 mm in diameter) ofthe cellulose acylate film of the invention is conditioned at 25° C. and90% RH and 95% RH each for 24 hours and then the moisture content perunit area (g/m²) is calculated in accordance with JIS Z-0208 by using avapor transmission rate tester “KK-709007” (manufactured by TOYO SEIKI).Then the vapor transmission rate is determined as follows: vaportransmission rate=(mass after conditioning)−(mass before conditioning).

In the case of using the cellulose acylate film of the invention as atransparent protective film for a polarizing plate, alkalisaponification of the cellulose acylate film surface may be cited as aneffective means of laminating the cellulose acylate film on thepolarizing plate. By the alkali saponification, the cellulose acylatefilm surface becomes hydrophilic and the contact angle to water isreduced. It is preferable that the contact angle of thealkali-saponified cellulose acylate film of the invention is from 95% to0% of the contact angle of the cellulose acylate film not containing theadditive. It is still preferable that the former contact angle is from90% to 0%, more preferably from 85% to 0%, of the latter. To evaluatethe contact angle, the hydrophilic/hydrophobic nature is examined by aconventionally employed method which comprises dropping a water dropletof 3 mm in diameter on the surface of the alkali-saponified film andmeasuring the angle between the film surface and the water droplet.

It is preferable that the tear strength of the cellulose acylate filmcontaining the additive of the invention is not more than 95% of thetear strength of the cellulose acylate film not containing the additive.It is still preferable that the former tear strength is from 5 to 90%,more preferably from 10 to 85%, of the latter. To achieve stablehandling properties during the film production and polarizing plateprocessing, a film should have an appropriate hardness, which can bealmost substituted by the tear strength of the film. So long as the tearstrength of the cellulose acylate film containing the additive is notless than the lower limit as defined above, there arises no such problemin the production that the film easily tears in the course of theproduction. On the other hand, it is preferable that the tear strengthis not less than the upper limit as defined above, since there arises nosuch problem that the film becomes too hard and thus suffers fromtroubles in traveling along a curved roll during the film production andpolarizing plate processing. The tear strength can be determined inpractice in accordance with the tear test as defined in JISK-7128-2:1998 (Elmendorf tear method) comprising conditioning a samplepiece (50 mm×64 mm) at 25° C. and 65% RH for 2 hours and then measuringthe tear strength with the use of a light-load tear strength tester.

It is preferable that the coefficient of humidity expansion of thecellulose acylate film containing the additive of the invention is from95% to 0% of the coefficient of humidity expansion of the celluloseacylate film not containing the additive. It is still preferable thatthe former coefficient of humidity expansion is from 90% to 0%, morepreferably from 85% to 0%, of the latter. Coefficient of humidityexpansion means a change in the length of a sample caused by a change inthe relative humidity at a constant temperature. By controllingcoefficient of humidity expansion, frame-shaped increase intransmittance, i.e., light leakage caused by strain can be prevented inthe case of using the cellulose acylate film of the invention as amember of a liquid crystal display. The coefficient of humidityexpansion is measured in practice by preparing a sample (20×5 mm),increasing the humidity from 15% RH to 90% RH at a constant temperatureof 60° C. and employing the value at 60% RH.

(Cellulose Acylate) (Starting Cotton Material for Synthesizing CelluloseAcylate)

Examples of the starting cellulose to be used for synthesizing thecellulose acylate in the invention include cotton linter and wood pulp(hardwood pulp and softwood pulp). Use can be made of cellulose acylateobtained from any cellulose material and a mixture is also usable insome cases. These starting cotton materials are described in detail in,for example, Purasuchikku Zairyo Koza (17), Senisokei Jushi (Marusawaand Uda, The Nikkan Kogyo Shinbun, Ltd., 1970) and Japan Institute ofInvention and Innovation Journal of Technical Disclosure No. 2001-1745,p. 7 to 8, though the material of the cellulose acylate film of theinvention is not particularly restricted thereto.

(Degree of Substitution in Cellulose Acylate)

A cellulose acylate which is produced starting with the cellulosematerial as described above will be illustrated. In the celluloseacylate in the invention, hydroxyl groups in cellulose have beenacylated. As the substituents, use may be made of acetyl groups havingfrom 2 to 22 carbon atoms. In the cellulose acylate to be used in theinvention, the degree of substitution of hydroxyl groups in thecellulose is not particularly restricted. The substitution degree can bedetermined by measuring the degree of binding of acetic acid and/orfatty acids having from 3 to 22 carbon atoms substituting hydroxylgroups in cellulose and calculating. The measurement can be carried outin accordance with ASTM D-817-91.

In the cellulose acylate film of the invention, Re and Rth originatingin the cellulose main chain can be more compensated by acyl substituentside chains at a higher acylation ratio, thereby lowering Re and Rth.That is to say, the amount of the compound capable of lowering Rth as anadditive can be lowered by using cellulose acylate having a highacylation ratio as the starting material (starting polymer) and, in itsturn, an extreme lowering in Tg caused by the excessive use of theadditive can be prevented. More specifically speaking, it is preferablethat the acylation ratio of the starting polymer for the celluloseacylate film of the invention is from 2.85 to 3.00, more preferably from2.90 to 3.00. The term “acylation ratio” as used herein means the totaldegree of substitution, i.e., indicating the sum of the substitutiondegrees in the case of having a mixture of substituents of differenttypes.

Among the acetic acid or fatty acids having from 3 to 22 carbon atomssubstituting hydroxyl groups in cellulose, the acyl group having from 2to 22 carbon atoms may be an aliphatic group or an allyl group withoutrestriction. Either a single group or a mixture of two or more groupsmay be used. Use may be made of, for example, alkylcarbonyl esters,alkenylcarbonyl esters, aromatic carbonyl esters and aromaticalkylcarbonyl esters of cellulose each optionally having additionalsubstituents. Preferable examples of the acyl group include acetyl,propionyl, butanoyl, heptanoyl, hexanoyl, octanoyl, decanoyl,dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl,i-butanoyl, t-butanoyl, cyclohexanecarbonyl, oleoyl, benzoyl,naphthylcarbonyl and cinnamoyl groups. Among them, acetyl, propionyl,butanoyl, dodecanoyl, octadecanoyl, t-butanoyl, oleoyl, benzoyl,naphthylcarbonyl and cinnamoyl groups are preferable, and acetyl,propionyl and butanoyl groups are more preferable.

(Organic Solvent of Cellulose Acylate Solution)

In the invention, it is preferred to produce the cellulose acylate filmby the solvent casting method. In this method, a film is produced byusing a cellulose acylate solution dissolved in an organic solvent (adope). As preferable examples of organic solvents to be used as the mainsolvent in the invention, use may be preferably made of solventsselected from among esters, ketones and ethers having from 3 to 12carbon atoms and halogenated hydrocarbons having from 3 to 12 carbonatoms and halogenated hydrocarbons having form 1 to 7 carbon atoms.These esters, ketones and ethers may have cyclic structure. It is alsopossible to use, as the main solvent, compounds having two or morefunctional groups (i.e., —O—, —CO— and —COO—) of esters, ketones andethers and these compounds may have another functional group such asalcoholic hydroxyl group at the same time. In the case of a main solventhaving two or more types of functional groups, the carbon atom numberfalling within the range as specified above concerning a compound havingone of the functional groups.

As described above, the cellulose acylate film according to theinvention may comprise, as the main solvent, either a chlorine-basedhalogenated hydrocarbon or a nonchlorinated organic solvent as describedin Japan Institute of Invention and Innovation Journal of TechnicalDisclosure No. 2001-1745 (p. 12 to 16). The invention is not restrictedthereto.

Other solvents for the cellulose acylate solution and film according tothe invention and dissolution methods therefore are disclosed in thefollowing patents which are preferred embodiments: for example,JP-A-2000-95876, JP-A-12-95877, JP-A-10-324774, JP-A-8-152514,JP-A-10-330538, JP-A-9-95538, JP-A-9-95557, JP-A-10-235664,JP-A-12-63534, JP-A-11-21379, JP-A-10-182853, JP-A-10-278056,JP-A-10-279702, JP-A-10-323853, JP-A-10-237816, JP-A-11-60807,JP-A-11-152342, JP-A-11-292988, JP-A-11-60752 and so on. According tothese patents, not only preferable solvents but also solution propertiesthereof and substances to coexist are reported, thereby presentingpreferred embodiments of the invention.

(Process for Producing Cellulose Acylate Film) (Dissolution Step)

In preparing a cellulose acylate solution (dope) of the invention, thecellulose acylate is dissolved by an arbitrary method withoutrestriction, i.e., by room-temperature dissolution, cold dissolution,hot dissolution or a combination thereof. Concerning the preparation ofthe cellulose acylate solution according to the invention, concentrationof the solution in association with the dissolution and filtration, itis preferable to employ the process described in, for example, JapanInstitute of Invention and Innovation Journal of Technical DisclosureNo. 2001-1745 (2001 Mar. 15, Japan Institute of Invention andInnovation), p. 22 to 25.

(Transparency of Dope Solution)

It is preferable that the transparency of the dope of the celluloseacylate solution according to the invention is 85% or higher, morepreferably 88% or higher and more preferably 90% or higher. In theinvention, it is confirmed that various additives have been sufficientlydissolved in the cellulose acylate dope solution. The dope transparencyin practice is determined by pouring the dope solution into a glass cell(1 cm×1 cm), measuring the absorbance at 550 nm with a spectrophotometer(UV-3150, manufactured by Shimadzu), separately measuring the solventalone as a blank, and then calculating the transparency based on theratio to the absorbance of the blank.

(Casting, Drying and Winding Steps)

Next, a method of producing a film by using the cellulose acylatesolution (dope) of the invention will be illustrated.

Concerning a film-forming method and apparatus for producing thecellulose acylate film of the invention, use can be made of the solventcast film-forming method and a solvent cast film-forming apparatusconventionally employed in forming cellulose triacetate films. A dope (acellulose acylate solution) prepared in a dissolution machine (a pot) isonce stored in a storage pot and, after defoaming, the dope is subjectedto the final preparation. Then the dope is discharged from a dopeexhaust and fed into a pressure die via, for example, a pressureconstant-rate pump whereby the dope can be fed at a constant rate at ahigh accuracy depending on the rotational speed. From the pipe sleeve(slit) of the pressure die, the dope is uniformly cast onto a metallicsupport continuously running in the casting section. At the peelingpoint where the metallic support has almost rounded, the half-dried dopefilm (also called a web) is stripped off from the metallic support.

In the step or stripping off from the support, the degree of the dryingand volatilization (the degree of half-drying) affects the physicalproperties of the final film product. More specifically speaking, thecrystallization of the polymer chain proceeds to the higher extent at ahigher drying speed and, as a result, the film becomes relatively hard.In such a case, the film properties such as dimensional change can bemore improved. In the case where the film having been almost dried isstripped and then dried slowly, on the contrary, the crystallization ofthe polymer chain less proceeds and thus the film becomes relativelysoft. To obtain a highly crystallized film showing an X-ray diffractionpattern falling within the desired range, it is preferred in theinvention to strip off the film wherein the amount of the solventremaining therein is 50% or more but not more than 200%. It is preferredthat the amount of the solvent remaining at the stripping is 55% or morebut not more than 180%, more preferably 60% or more but not more than150%. The amount of the remaining solvent is represented by thefollowing numerical formula (9). The remaining volatile mass means thevalue determined by subtracting the mass of the heated (2 hours at 120°C.) film from the film mass before heating.

amount of remaining solvent=(remaining volatile mass/heated filmmass)×100(%)  Numerical formula (9)

The obtained web is clipped at both ends and dried by carrying with atenter while maintaining the width at a constant level. Subsequently, itis carried with rolls in a dryer to terminate the drying and then woundwith a winder in a definite length.

Although the drying temperature may be optionally varied, it is foundout that the optical performance of the cellulose acylate film of theinvention can be controlled by drying at a higher temperature. By dryingat a higher temperature, namely, the main chain and side chains ofcellulose acylate are easily loosened. In particular, the degrees offreedom of side chains are elevated and thus the orientation in the filmplane and the planar orientation in the film thickness direction areregulated. As a result, it becomes possible to lower both of Re and Rth.More specifically speaking, it is preferable to dry the film at 120 to160° C., more preferably at 125 to 160° C. and more preferably at 130 to160° C. By employing such drying conditions, the amount of the compoundcapable of lowering Rth as an additive can be lowered and, in its turn,an extreme lowering in Tg caused by the excessive use of the additivecan be prevented.

Combination of the tenter and the rolls in the dryer may vary dependingon the purpose. In the solvent cast film-forming method to producefunctional protective films for electronic displays or silver halidephotosensitive materials (i.e., the main uses of the cellulose acylatefilm of the invention), a coater is frequently employed, in addition tothe solvent cast film-forming apparatus, so as to process the filmsurface by providing, for example, an undercoating layer, an antistaticlayer, an anti-halation layer or a protective layer. These layers aredescribed in detail in Japan Institute of Invention and InnovationJournal of Technical Disclosure No. 2001-1745 (2001 Mar. 15, JapanInstitute of Invention and Innovation), p. 25 to 30. The techniquesgiven in this document, which are itemized as casting (includingco-casting), metallic supports, drying, peeling and so on, arepreferably usable in the invention.

(Additives to Cellulose Acylate)

To a cellulose acylate solution of the invention, it is possible to addvarious additives (for example, a compound capable of lowering Rth, awavelength dispersion regulator, a UV-blocking agent, a plasticizer, anantidegradant, fine particles, an optical characteristic-controllingagent, etc.) depending on purpose in individual steps of the production.Now, these additives will be illustrated. These additives may be addedin the step of preparing the dope. Alternatively, a step of adding theadditives may be provided in the final step of preparing the dope.

(Compound capable of lowering Rth)

It is preferable that the cellulose acylate film of the inventioncontains at least one compound lowering the retardation value in thefilm thickness direction Rth (hereinafter referred to as a compoundcapable of lowering Rth) within a range fulfilling the followingnumerical formulae (3) and (4):

(Rth _(λA) −Rth _(λ0))/A≦<−1.0  Numerical formula (3)

0.01≦A≦30.  Numerical formula (4)

It is preferable that the above numerical formulae (3) and (4) are:

(Rth _(λA) −Rth _(λ0))/A≦−2.0  Numerical formula (3-1)

(X)0.01≦A≦20.  Numerical formula (4-1)

It is still preferable that the above numerical formulae (3) and (4)are:

(Rth _(λA) −Rth _(λ0))/A≦−3.0  Numerical formula (3-2)

0.01≦A≦15.  Numerical formula (4-2)

In the above formulae, Rth_(λA) is Rth (nm) of a film containing A % bymass of the compound lowering Rth_(λ); Rth_(λ0) is Rth (nm) of a filmcontaining no compound lowering Rth_(λ); and A is the mass (%) of thecompound lowering Rth_(λ) referring the mass of the starting polymer forthe film as to 100

(Structural Characteristic of Rth-Lowering Agent)

Now, the compound capable of lowering Rth of cellulose acylate film willbe illustrated.

To sufficiently lower the optical anisotropy and reduce both of Re andRth close to zero, it is preferable to use a compound inhibiting theorientation of cellulose acylate in a film in plane and in the filmthickness direction. For this purpose, it is advantageous to employ acompound lowering optical anisotropy which is sufficiently compatiblewith cellulose acylate and has neither a rod-like structure nor a planarstructure by itself. In the case of having a plural number of planarfunctional groups such as aromatic groups, more specifically speaking, anonplaner structure having these functional groups not on a single planeis advantageous.

(Log P Value)

To produce the cellulose acylate film of the invention, it is preferableto employ, from among the compounds which prevent cellulose acylate inthe film from orientation in-plane and in the film thickness directionto thereby lower Rth, a compound having an octanol-water partitioncoefficient (log P value) of from 0 to 7. A compound having a logp valuenot more than 7 has an excellent compatibility with cellulose acylateand thus never results in clouding or blooming of the film. A compoundhaving a log P value not less than 0 has not excessively highlyhydrophilic nature and thus never causes problems such as worsening thewater resistance of the cellulose acylate film. It is still preferablethat the log P value ranges from 1 to 6, especially preferably from 1.5to 5.

The octanol-water partition coefficient (log P value) can be measured bythe flask shaking method in accordance with JIS Z7260-107 (2000). It isalso possible to estimate the octanol-water partition coefficient (log Pvalue) by using not practical measurement but a computational orempirical method. As the computational method, use may be preferablymade of Crippen's fragmentation method (J. Chem. Inf. Comput. Sci., vol.27, p. 21 (1987)), Viswanadhan's fragmentation method (J. Chem. Inf.Comput. Sci., vol. 29, p. 163 (1989)), Broto's fragmentation method(Eur. J. Med. Chem.—Chim. Theor., vol. 19, p. 71 (1984)) and so on. Itis still preferable to employ Crippen's fragmentation method. In thecase where the log P value of a compound determined by the measurementmethod differs from its calculated value, it is favorable to judgewhether or not the compound falls within the desired range with the useof Crippen's fragmentation method.

(Physical Properties of Rth-Lowering Agent)

The Rth-lowering agent may either contain an aromatic group or not. Itis preferable that the Rth-lowering agent has a molecular weight of 150or more but not more than 3000, more preferably 170 or more but not morethan 2000 and more preferably 200 or more but not more than 1000. Solong as the molecular weight falls within this range, the compound mayhave either a specific monomer structure or an oligomer or polymerstructure composed of a plural number of the monomer units bondedtogether.

It is preferable that the Rth-lowering agent is a liquid at 25° C. or asolid having a melting point of from 25 to 250° C. A compound which is aliquid at 25° C. or a solid having a melting point of from 25 to 200° C.is still preferred. It is also preferable that the Rth-lowering agentwould not vaporize in the course of dope casting and drying inconstructing the cellulose acylate film.

The Rth-lowering agent is added preferably in an amount of from 0.01 to30% by mass, more preferably from 0.05 to 25% by mass and particularlypreferably from 0.1 to 20% by mass based on the cellulose acylate.

A single compound may be used as the Rth-lowering agent. Alternatively,use can be made of a mixture of two or more compounds at an arbitraryratio. The Rth-lowering agent may be added at any step in preparing adope. It may be added at the final step of the dope preparation.

Preferable examples of the Rth-lowering agent include compoundsrepresented by the following formula (1). Next, the compounds of theformula (1) will be described.

In the formula (1), R¹¹ represents an alkyl group or an aryl group; andR¹² and R¹³ each independently represents a hydrogen atom, an alkylgroup or an aryl group. It is preferable that the sum of the carbonatoms in R¹¹, R¹² and R¹³ is 10 or more. These alkyl and aryl groups mayhave substituents.

Preferable examples of the substituents include a fluorine atom, alkylgroups, aryl groups, alkoxy groups, sulfone group and sulfonamido group.Among all, alkyl groups, aryl groups, alkoxy groups, sulfone group andsulfonamido group are particularly preferable The alkyl group may beeither chain type, branched or cyclic. It is preferable that the alkylgroup has from 1 to 25 carbon atoms, more preferably from 6 to 25 carbonatoms and especially preferably from 6 to 20 carbon atoms (for example,methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, amyl,isoamyl, t-amyl, hexyl, cyclohexyl, heptyl, octyl, bicyclooctyl, nonyl,adamantyl, decyl, t-octyl, undecyl, dodecyl, tridecyl, tetradecyl,pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and didecyl).

The aryl group preferably has from 6 to 30 carbon atoms, more preferablyfrom 6 to carbon atoms (for example, phenyl, biphenyl, terphenyl,naphthyl, binaphthyl and triphenylphenyl). Next, preferable examples ofthe compounds represented by the formula (1) will be presented, thoughthe invention is not restricted to these specific examples.

As examples of the Rth-lowering agent, compounds represented by thefollowing formula (2) may be also cited.

In the formula (2), R²¹ represents an alkyl group or an aryl group, andR²² and R²³ each independently represents a hydrogen atom, an alkylgroup or an aryl group. The alkyl group may be either chain type,branched or cyclic. It is preferable that the alkyl group has from 1 to20 carbon atoms, more preferably from 1 to 15 carbon atoms andespecially preferably from 1 to 12 carbon atoms. As a cyclic alkylgroup, a cyclohexyl group is particularly preferred. It is preferablethat the aryl group has from 6 to 36 carbon atoms, more preferably from6 to 24 carbon atoms. It is preferable that the sum of the carbon atomsin R²¹ and R²² is 10 or more. These alkyl and aryl groups may havesubstituents.

The above alkyl and aryl groups may have substituents and preferableexamples of the substituents include halogen atoms (for example,chlorine, bromine, fluorine and iodine), alkyl groups, aryl groups,alkoxy groups, aryloxy groups, acyl groups, alkoxycarbonyl groups,aryloxycarbonyl groups, acyloxy groups, sulfonylamino groups, hydroxygroup, cyano group, amino group and acylamino groups. Still preferableexamples thereof include halogen atoms, alkyl groups, aryl groups,alkoxy groups, aryloxy groups, sulfonylamino groups and acylaminogroups. Particularly preferable examples thereof include alkyl groups,aryl groups, sulfonylamino groups and acylamino groups.

Next, preferable examples of the compounds represented by the formula(2) will be presented, though the invention is not restricted to thesespecific examples.

(Wavelength Dispersion Regulator)

It is preferable that the cellulose acylate film of the inventioncontains at least one compound capable of lessening |Re₄₀₀−Re₇₀₀| and|Rth₄₀₀−Rth₇₀₀|, i.e., a compound capable of lessening the wavelengthdispersion of retardation (hereinafter referred to as a wavelengthdispersion regulator) in an amount of from 0.01 to 30% by mass based onthe solid content of the polymer material of the cellulose acylate film.Next, the wavelength dispersion regulator will be illustrated.

To improve the wavelength dispersion of Rth of the cellulose acylatefilm of the invention, it is preferable that the film contains at leastone compound lowering the wavelength dispersion of Rth (ΔRth)represented by the following numerical formula (6) (a wavelengthdispersion regulator) within a range of fulfilling the followingnumerical formulae (7) and (8).

ΔRth=|Rth ₄₀₀ −Rth ₇₀₀|  Numerical formula (6)

(ΔRth _(B) ΔRth ₀)/B<−2.0  Numerical formula (7)

0.01≦B≦30.  Numerical formula (8)

Concerning the above numerical formulae (7) and (8), it is stillpreferable:

(ΔRth _(B) ΔRth ₀)/B≦−3.0  Numerical formula (7-2)

0.05≦B≦25.  Numerical formula (8-2)

And it is still preferable:

(ΔRth _(B) −ΔRth ₀)/B≦−4.0  Numerical formula (7-3)

0.1≦B≦20.  Numerical formula (8-3)

In the above formulae, ΔRth_(B) is ΔRth (nm) of a film containing B % bymass of a wavelength dispersion regulator. ΔRth(0) is ΔRth (nm) of afilm containing no wavelength dispersion regulator. B is the mass (%) ofthe wavelength dispersion regulator referring the mass of the polymeremployed as the film material as to 100.

(Method of Adding Wavelength Dispersion Regulator)

As the wavelength dispersion regulator, a single compound may be used.Alternatively, use can be made of a mixture of two or more compounds atan arbitrary ratio. The wavelength dispersion regulator may be added atany step during the production of a dope. It may be added at the finalsate of the dope preparation step.

Specific examples of the wavelength dispersion regulator preferablyusable in the invention include benzotriazole compounds, benzophenonecompounds, cyano-containing compounds, oxobenzophenone compounds,salicylic acid ester compounds, nickel complex salt compounds and so onthough the invention is not restricted to these compounds

As the benzotriazole compounds, those represented by the formula (3) arepreferably usable as the wavelength dispersion regulator in theinvention.

Q³¹-Q³²-OH  Formula (3)

In the above formulae, Q³¹ represents a nitrogen-containing aromaticheterocycle, while Q³² represents an aromatic ring.

Q³¹ represents a nitrogen-containing aromatic heterocycle, preferably a5- to 7-membered nitrogen-containing aromatic heterocycle and morepreferably a 5- or 6-membered nitrogen-containing aromatic heterocyclesuch as imidazole, pyrazole, triazole, tetrazole, thiazole oxazole,selenazole, benzotriazole, benzothiazole, benzoxaxzole, benzoselenazole,thiadiazole, oxadiazole, naphthothiazole, naphtooxazole,azabenzimidazole, purine, pyridine, pyrazine, pyrimidine, pyridazine,triazine, triazaindene, tetrazaindene and so on. More preferably, Q³¹represents a 5-membered nitrogen-containing aromatic heterocycle such asimidazole, pyrazole, triazole, tetrazole, thiazole, oxazole,benzotriazole, benzothiazole, benzoxazole, thiadiazole or oxadiazole,and benzotriazole is particularly preferable.

The nitrogen-containing aromatic heterocycle represented by Q³¹ may havea substituent and examples of the substituent include the substituent Twhich will be described hereinafter. In the case of having a pluralnumber of substituents, these substituents may be fused together to forman additional ring.

The aromatic ring represented by Q³² may be either an aromatichydrocarbon ring or an aromatic heterocycle. It may be a single ring orit may form a fused ring together with another ring.

Preferable examples of the aromatic hydrocarbon ring include monocyclicor bicyclic aromatic hydrocarbon rings having from 6 to 30 carbon atoms(for example, benzene ring, naphthalene ring and so on), more preferablyan aromatic hydrocarbon ring having from 6 to 20 carbon atoms and morepreferably an aromatic hydrocarbon ring having from 6 to 12 carbonatoms. A benzene ring is the most desirable one.

Preferable examples of the aromatic heterocycle include nitrogenatom-containing or sulfur atom-containing aromatic heterocycles.Specific examples of the heterocycle include thiophene, imidazole,pyrazole, pyridine, pyrazine, pyridazine, triazole, trizine, indole,indazole, purine, thiazoline, thiazole, thiadiazole, oxazoline, oxazole,oxadiazole, quinoline, isoquinoline, phthalazine, naphthylidine,quinoxaline, quinazoline, cinnoline, pteridine, acridine,phenanthridine, phenazine, tetrazole, benzimidazole, benzoxazole,benzthiazole, benzotriazole, tetrazaindene and so on. Preferableexamples of the aromatic heterocycles include pyridine, triazine andquinoline.

The aromatic ring represented by Q³² is preferably an aromatichydrocarbon ring, more preferably a naphthalene ring or a benzene ringand particularly preferably a benzene ring. Q³² may have a substituentand examples of the substituent include the substituent T which will bedescribed hereinafter.

Examples of the substituent T include alkyl groups (preferably havingfrom 1 to 20 carbon atoms, more preferably from 1 to 12 carbon atoms andparticularly preferably from 1 to 8 carbon atoms, such as methyl, ethyl,isopropyl, tert-butyl, n-octyl, n-decyl, n-hexadecyl, cyclopropyl,cyclopentyl and cyclohexyl), alkenyl groups (preferably having from 2 to20 carbon atoms, more preferably from 2 to 12 carbon atoms andparticularly preferably from 2 to 8 carbon atoms, such as vinyl, allyl,2-butenyl and 3-pentenyl), alkynyl groups (preferably having from 2 to20 carbon atoms, more preferably from 2 to 12 carbon atoms andparticularly preferably from 2 to 8 carbon atoms, such as propargyl and3-pentynyl), aryl groups (preferably having from 6 to 30 carbon atoms,more preferably from 6 to 20 carbon atoms and particularly preferablyfrom 6 to 12 carbon atoms, such as phenyl, p-methylphenyl and naphthyl),substituted or unsubstituted amino groups (preferably having from 0 to20 carbon atoms, more preferably from 0 to 10 carbon atoms andparticularly preferably from 0 to 6 carbon atoms, such as amino,methylamino, dimethylamino, diethylamino and dibenzylamino), alkoxygroups (preferably having from 1 to 20 carbon atoms, more preferablyfrom 1 to 12 carbon atoms and particularly preferably from 1 to 8 carbonatoms, such as methoxy, ethoxy and butoxy), aryloxy groups (preferablyhaving from 6 to 20 carbon atoms, more preferably from 6 to 16 carbonatoms and particularly preferably from 6 to 12 carbon atoms, such asphenyloxy and 2-naphthyloxy), acyl groups (preferably having from 1 to20 carbon atoms, more preferably from 1 to 16 carbon atoms andparticularly preferably from 1 to 12 carbon atoms, such as acetyl,benzoyl, formyl and pivaloyl), alkoxycarbonyl groups (preferably havingfrom 2 to 20 carbon atoms, more preferably from 2 to 16 carbon atoms andparticularly preferably from 2 to 12 carbon atoms, such asmethoxycarbonyl and ethoxycarbonyl), aryloxycarbonyl groups (preferablyhaving from 7 to 20 carbon atoms, more preferably from 7 to 16 carbonatoms and particularly preferably from 7 to 10 carbon atoms, such asphenyoxycarbonyl), acyloxy groups (preferably having from 2 to 20 carbonatoms, more preferably from 2 to 16 carbon atoms and particularlypreferably from 2 to 10 carbon atoms, such as acetoxy and benzoyloxy),acylamino groups (preferably having from 2 to 20 carbon atoms, morepreferably from 2 to 16 carbon atoms and particularly preferably from 2to 10 carbon atoms, such as acetylamino and benzoylamino),alkoxycarbonylamino groups (preferably having from 2 to 20 carbon atoms,more preferably from 2 to 16 carbon atoms and particularly preferablyfrom 2 to 12 carbon atoms, such as methoxycarbonylamino),aryloxycarbonylamino groups (preferably having from 7 to 20 carbonatoms, more preferably from 7 to 16 carbon atoms and particularlypreferably from 7 to 12 carbon atoms, such as phenyloxycarbonylamino),sulfonylamino groups (preferably having from 1 to 20 carbon atoms, morepreferably from 1 to 16 carbon atoms and particularly preferably from 1to 12 carbon atoms, such as methanesulfonylamino andbenzenesulfonylamino), sulfamoyl groups (preferably having from 0 to 20carbon atoms, more preferably from 0 to 16 carbon atoms and particularlypreferably from 0 to 12 carbon atoms, such as sulfamoyl,methylsulfamoyl, dimethylsulfamoyl and phenylsulfamoyl), carbamoylgroups (preferably having from 1 to 20 carbon atoms, more preferablyfrom 1 to 16 carbon atoms and particularly preferably from 1 to 12carbon atoms, such as carbamoyl, methylcarbamoyl, diethylcarbamoyl andphenylcarbamoyl), alkylthio groups (preferably having from 1 to 20carbon atoms, more preferably from 1 to 16 carbon atoms and particularlypreferably from 1 to 12 carbon atoms, such as methyltio and ethylthio),arylthio groups (preferably having from 6 to 20 carbon atoms, morepreferably from 6 to 16 carbon atoms and particularly preferably from 6to 12 carbon atoms, such as phenylthio), sulfonyl groups (preferablyhaving from 1 to 20 carbon atoms, more preferably from 1 to 16 carbonatoms and particularly preferably from 1 to 12 carbon atoms, such asmesyl and tosyl), sulfinyl groups (preferably having from 1 to 20 carbonatoms, more preferably from 1 to 16 carbon atoms and particularlypreferably from 1 to 12 carbon atoms, such as methanesulfinyl andbenzenesulfinyl), ureido groups (preferably having from 1 to 20 carbonatoms, more preferably from 1 to 16 carbon atoms and particularlypreferably from 1 to 12 carbon atoms, such as ureido, methylureido andphenylureido), phosphoramido groups (preferably having from 1 to 20carbon atoms, more preferably from 1 to 16 carbon atoms and particularlypreferably from 1 to 12 carbon atoms, such as diethylphosphoramido andphenylphosphoramido), hydroxy group, mercapto group, halogen atoms (forexample, fluorine atom, chlorine atom, bromine atom and iodine atom),cyano group, sulfo group, carboxyl group, nitro group, hydroxamategroup, sulfino group, hydrazino group, imino group, heterocyclic groups(preferably having from 1 to 30 carbon atoms, more preferably from 1 to12 carbon atoms, and having a nitrogen atom, an oxygen atom or a sulfuratom as a hetero atom, such as imidazolyl, pyridyl, quinolyl, furyl,piperidyl, morpholino, benzoxazolyl, benzimidazolyl and benzthiazolyl),silyl groups (preferably having from 3 to 40 carbon atoms, morepreferably from 3 to 30 carbon atoms and particularly preferably from 3to 24 carbon atoms, such as tirmethylsilyl and triphenylsilyl) and soon. These substituents may be further substituted. In the case of havingtwo or more substituent, the substituents may be either the same ordifferent. If possible, these substituents may be bonded together tofrom a ring.

As the compounds represented by the formula (3), compounds representedthe following formula (3-1) are preferable.

In the above formula, R³¹, R³², R³³, R³⁴, R³⁵, R³⁶, R³⁷ and R³⁸independently represent each a hydrogen atom or a substituent. As thesubstituent, the above-described substituents T may be used. Thesesubstituents may be further substituted by another substituent andsubstituents may be fused together to form a cyclic structure.

R³¹ and R³³ preferably represent each a hydrogen atom, an alkyl group,an alkenyl group, an alkynyl group, an aryl group) a substituted orunsubstituted amino group, an alkoxy group, an aryloxy group, a hydroxygroup or a halogen atom. It more preferably represents a hydrogen atom,an alkyl group, an aryl group, an aryloxy group or a halogen atom, morepreferably a hydrogen atom or an alkyl group having from 1 to 12 carbonatoms and particularly preferably an alkyl group having from 1 to 12(preferably from 4 to 12) carbon atoms.

R³² and R³⁴ preferably represent each a hydrogen atom, an alkyl group,an alkenyl group, an alkynyl group, an aryl group, a substituted orunsubstituted amino group, an alkoxy group, an aryloxy group, a hydroxygroup or a halogen atom. It more preferably represents a hydrogen atom,an alkyl group, an aryl group, an alkyloxy group, an aryloxy group or ahalogen atom, more preferably a hydrogen atom or an alkyl group havingfrom 1 to 12 carbon atoms, particularly preferably a hydrogen atom or amethyl group and most desirably a hydrogen atom.

R³⁵ and R³⁶ preferably represent each a hydrogen atom, an alkyl group,an alkenyl group, an alkynyl group, an aryl group, a substituted orunsubstituted amino group, an alkoxy group, an aryloxy group, a hydroxygroup or a halogen atom. It more preferably represents a hydrogen atom,an alkyl group, an aryl group, an alkyloxy group, an aryloxy group or ahalogen atom, more preferably a hydrogen atom or an alkyl group havingfrom 1 to 12 carbon atoms, particularly preferably a hydrogen atom or amethyl group and most desirably a hydrogen atom.

R³⁶ and R³⁷ preferably represent each a hydrogen atom, an alkyl group,an alkenyl group, an alkynyl group, an aryl group, a substituted orunsubstituted amino group, an alkoxy group, an aryloxy group, a hydroxygroup or a halogen atom. It more preferably represents a hydrogen atom,an alkyl group, an aryl group, an alkyloxy group, an aryloxy group or ahalogen atom, more preferably a hydrogen atom or a halogen atom andparticularly preferably a hydrogen atom or a chlorine atom.

As the compounds represented by the formula (3), compounds representedthe following formula (3-2) are still preferable.

Formula (3-2):

In the above formula, R³¹, R³³, R³⁶ and R³⁷ have the same meanings asdefined in the formula (3-1). Preferable ranges thereof are also thesame.

Next, preferable examples of the compounds represented by the formula(3) will be presented, though the invention is not restricted to thesespecific examples.

It is confirmed that the cellulose acylate film of the inventionproduced by using a benzotriazole compound having a molecular weight of320 or more, from among the benzotriazole compounds presented above, isadvantageous from the viewpoint of retention.

As a benzophenone compound which is one of the wavelength dispersionregulators usable in the invention, it is preferable to employ acompound represented by the following formula (4).

In the above formula, Q⁴¹ and Q⁴² independently represent each anaromatic ring. X⁴¹ represents NR⁴¹ (wherein R⁴¹ represents a hydrogenatom or a substituent), an oxygen atom or a sulfur atom.

The aromatic rings represented by Q⁴¹ and Q⁴² may be either aromatichydrocarbon rings or aromatic heterocycles. They may be a single ring orfoim a flsed ring together with another ring.

Preferable examples of the aromatic hydrocarbon ring represented by Q⁴¹and Q⁴² include monocyclic or bicyclic aromatic hydrocarbon rings havingfrom 6 to 30 carbon atoms (for example, benzene ring, naphthalene ringand so on), more preferably an aromatic hydrocarbon ring having from 6to 20 carbon atoms and more preferably an aromatic hydrocarbon ringhaving from 6 to 12 carbon atoms. A benzene ring is the most desirableone.

Preferable examples of the aromatic heterocycle represented by Q⁴¹ andQ⁴² include aromatic heterocycles containing at least one of oxygen,nitrogen and sulfur atoms. Specific examples of the heterocycle includefuran, pyrrole, thiophene, imidazole, pyrazole, pyridine, pyrazine,pyridazine, triazole, triazine, indole, indazole, purine, thiazoline,thiazole, thiadiazole, oxazoline, oxazole, oxadiazole, quinoline,isoquinoline, phthalazine, naphthylidine, quinoxaline, quinazoline,cinnoline, pteridine, acridine, phenanthridine, phenazine, tetrazole,benzimidazole, benzoxazole, benzthiazole, benzotriazole, tetrazaindeneand so on. Preferable examples of the aromatic heterocycles includepyridine, triazine and quinoline.

The aromatic rings represented by Q⁴¹ and Q⁴² are each preferably anaromatic hydrocarbon ring, more preferably an aromatic hydrocarbon ringhaving from 6 to 10 carbon atoms and more preferably a substituted orunsubstituted benzene ring.

Q⁴¹ and Q⁴² may have a substituent and examples of the substituentinclude the substituent T as described above, provided that such asubstituent never contains carboxylic acid, sulfonic acid or aquaternary ammonium salt. If possible, substituents may be bondedtogether to form a cyclic structure.

X⁴¹ represents NR⁴¹ (wherein R⁴¹ represents a hydrogen atom or asubstituent which include the substituent T as described above), anoxygen atom or a sulfur atom. It is preferable that X⁴¹ is NR⁴² (whereinR⁴² preferably represents an acyl group or a sulfonyl group and such asubstituent may further have a substituent) or an oxygen atom. An oxygenatom is particularly preferred.

As the compounds represented by the formula (4), compounds representedthe following formula (4-1) are preferable.

In the above formula, R⁴¹¹, R⁴¹², R⁴¹³, R⁴¹⁴, R⁴¹⁵, R⁴¹⁶, R⁴¹⁷, R⁴¹⁸ andR⁴¹⁹ independently represent each a hydrogen atom or a substituent. Asthe substituent, the above-described substituents T may be used. Thesesubstituents may be further substituted by another substituent andsubstituents may be fused together to form a cyclic structure.

R⁴¹¹, R⁴¹³, R⁴¹⁴, R⁴¹⁵, R⁴¹⁶, R⁴¹⁸ and R⁴¹⁹ preferably represent each ahydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, anaryl group, a substituted or unsubstituted amino group, an alkoxy group,an aryloxy group, a hydroxy group or a halogen atom. It more preferablyrepresents a hydrogen atom, an alkyl group, an aryl group, an alkyloxygroup, an aryloxy group or a halogen atom, more preferably a hydrogenatom or an alkyl group having from 1 to 12 carbon atoms and particularlypreferably a hydrogen atom or a methyl group. A hydrogen atom is themost desirable one.

R⁴¹² preferably represents a hydrogen atom, an alkyl group, an alkenylgroup, an alkynyl group, an aryl group, a substituted or unsubstitutedamino group, an alkoxy group, an aryloxy group, a hydroxy group or ahalogen atom. It more preferably represents a hydrogen atom, an alkylgroup having from 1 to 20 carbon atoms, an amino group having from 0 to20 carbon atoms, an alkoxy group having from 1 to 12 carbon atoms, anaryloxy group having from 6 to 12 carbon atoms or a hydroxy group, morepreferably an alkoxy group having from 1 to 20 carbon atoms andparticularly preferably an alkoxy group having from 1 to 12 carbonatoms.

R⁴¹⁷ preferably represents a hydrogen atom, an alkyl group, an alkenylgroup, an alkynyl group, an aryl group, a substituted or unsubstitutedamino group, an alkoxy group, an aryloxy group, a hydroxy group or ahalogen atom. It more preferably represents a hydrogen atom, an alkylgroup having from 1 to 20 carbon atoms, an amino group having from 0 to20 carbon atoms, an alkoxy group having front 1 to 12 carbon atoms, anaryloxy group having from 6 to 12 carbon atoms or a hydroxy group, morepreferably a hydrogen atom or an alkyl group having from 1 to 20 carbonatoms (preferably from 1 to 12 carbon atoms, more preferably from 1 to 8carbon atoms, and more preferably a methyl group). A methyl group or ahydrogen atom is particularly preferred.

As the compounds represented by the formula (4), compounds representedthe following formula (4-2) are still preferable.

In the above formula, R⁴²⁰ represents a hydrogen atom, a substituted orunsubstituted alkyl group, a substituted or unsubstituted alkenyl group,a substituted or unsubstituted alkynyl group or a substituted orunsubstituted aryl group. As the substituent, the above-describedsubstituents T may be used. R⁴²⁰ preferably represents a substituted orunsubstituted alkyl group, more preferably a substituted orunsubstituted alkyl group, more preferably a substituted orunsubstituted alkyl group having from 5 to 20 carbon atoms, morepreferably a substituted or unsubstituted alkyl group having from 5 to12 carbon atoms (for example, n-hexyl, 2-ethylhexyl, n-octyl, n-decyl,n-dodecyl or benzyl group), and particularly preferably a substituted orunsubstituted alkyl group having from 6 to 12 carbon atoms (for example,2-ethylhexyl, n-octyl, n-decyl, n-dodecyl or benzyl group).

The compounds represented by the formula (4) can be synthesized by apublicly known method reported in JP-A-11-12219.

Next, specific examples of the compounds represented by the formula (4)will be presented, though the invention is not restricted to thesespecific examples.

In the invention, use can be also made of a cyano group-containingcompound as the wavelength dispersion regulator. As such a cyanogroup-containing compound, compounds represented by the formula (5) arepreferred.

In the above formula, Q⁵¹ and Q⁵² independently represent each anaromatic ring. X¹ and X² represent each a hydrogen atom or asubstituent, provided that at least one of them represents a cyanogroup, a carbonyl group, a sulfonyl group or an aromatic heterocycle.The aromatic rings represented by Q⁵¹ and Q⁵² may be either aromatichydrocarbon rings or aromatic heterocycles. They may be a single ring orform a fused ring together with another ring.

Preferable examples of the aromatic hydrocarbon ring include monocyclicor bicyclic aromatic hydrocarbon rings having from 6 to 30 carbon atoms(for example, benzene ring, naphthalene ring and so on), more preferablyan aromatic hydrocarbon ring having from 6 to 20 carbon atoms and morepreferably an aromatic hydrocarbon ring having from 6 to 12 carbonatoms. A benzene ring is the most desirable one.

Preferable examples of the aromatic heterocycle include aromaticheterocycles containing a nitrogen atom or a sulfur atom. Specificexamples of the heterocycle include thiophene, imidazole, pyrazole,pyridine, pyrazine, pyridazine, triazole, triazine, indole, indazole,purine, thiazoline, thiazole, thiadiazole, oxazoline, oxazole,oxadiazole, quinoline, isoquinoline, phthalazine, naphthylidine,quinoxaline, quinazoline, cinnoline, pteridine, acridine,phenanthridine, pbenazine, tetrazole, benzimidazole, benzoxazole,benzthiazole, benzotriazole, tetrazaindene and so on. Preferableexamples of the aromatic heterocycles include pyridine, triazine andquinoline.

The aromatic rings represented by Q⁵¹ and Q⁵² are each preferably anaromatic hydrocarbon ring, and more preferably a benzene ring. Q⁵¹ andQ⁵² may have a substituent and preferable examples of the substituentinclude the substituent T as described above.

X⁵¹ and X⁵² represent each a hydrogen atom or a substituent, providedthat at least one of them represents a cyano group, a carbonyl group, asulfonyl group or an aromatic heterocycle. As the substituentsrepresented by X⁵¹ and X⁵² may be the substituents T as described above.The substituents represented by X⁵¹ and X⁵² may be substituted byanother substituent. X⁵¹ and X⁵² may be fused to form a cyclicstructure.

Preferable examples of X⁵¹ and X⁵² include hydrogen atom, alkyl groups,aryl groups, cyano group, nitro group, carbonyl group, sulfonyl groupsand aromatic heterocycles, more preferably cyano group, carbonyl group,sulfonyl groups and aromatic heterocycles, more preferably cyano groupand carbonyl group, and particularly preferably cyano group andalkoxycarbonyl groups (—C(═O)OR⁵¹ wherein R⁵¹ represents an alkyl grouphaving from 1 to 20 carbon atoms, an aryl group having from 6 to 12carbon atoms or a combination thereof).

As the compounds represented by the formula (5), compounds representedthe following formula (5-1) are preferable.

In the above formula, R⁵¹¹, R⁵¹², R⁵¹³, R⁵¹⁴, R⁵¹⁵, R⁵¹⁶, R⁵¹⁷, R⁵¹⁸R⁵¹⁹ and R⁵²⁰ independently represent each a hydrogen atom or asubstituent. As the substituents, the substituent T as described abovemay be used. These substituents may be further substituted by anothersubstituent and substituents may be fused together to form a cyclicstructure. X⁵¹¹ and X⁵¹² respectively have the same meanings as X⁵¹ andX⁵² in the formula (5).

R⁵¹¹, R⁵¹², R⁵¹⁴, R⁵¹⁵, R⁵¹⁶, R⁵¹⁷, R⁵¹⁹ and R⁵²⁰ preferably representeach a hydrogen atom, an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a substituted or unsubstituted amino group, analkoxy group, an aryloxy group, a hydroxy group or a halogen atom. Itmore preferably represents a hydrogen atom, an alkyl group, an arylgroup, an alkyloxy group, an aryloxy group or a halogen atom, morepreferably a hydrogen atom or an alkyl group having from 1 to 12 carbonatoms and particularly preferably a hydrogen atom or a methyl group. Ahydrogen atom is the most desirable one.

R⁵¹³ and R⁵¹⁸ preferably represent each a hydrogen atom, an alkyl group,an alkenyl group, an alkynyl group, an aryl group, a substituted orunsubstituted amino group, an alkoxy group, an aryloxy group, a hydroxygroup or a halogen atom. It more preferably represents a hydrogen atom,an alkyl group having from 1 to 20 carbon atoms, an amino group havingfrom 0 to 20 carbon atoms, an alkoxy group having from 1 to 12 carbonatoms, an aryloxy group having from 6 to 12 carbon atoms or a hydroxygroup, more preferably a hydrogen atom, an alkyl group having form 1 to12 carbon atoms or an alkoxy group having from 1 to 12 carbon atoms, andparticularly preferably a hydrogen atom

As the compounds represented by the formula (5), compounds representedthe following formula (5-2) are still preferable.

In the above formula, R⁵¹³ and R⁵¹⁸ respectively have the same meaningsas those in the formula (5-1) and the preferable ranges thereof are alsothe same. X⁵¹³ represents a hydrogen atom or a substituent. As thesubstituent, the substituent T as described above may be used. Ifpossible, it may be further substituted by another substituents.

X⁵¹³ represents a hydrogen atom or a substituent and the above-describedsubstituent T may be used as the substituent. If possible, it may befurther substituted by another substituent. X⁵¹³ preferably represents ahydrogen atom, an alkyl group, an aryl group, a cyano group, a nitrogroup, a carbonyl group, a sulfonyl group or an aromatic heterocycle,more preferably a cyano group or a carbonyl group, and particularlypreferably a cyano group or an alkoxycarbonyl group (—C(═O)CR⁵² whereinR⁵² represents an alkyl group having from 1 to 20 carbon atoms, an arylgroup having from 6 to 12 carbon atoms or a combination thereof).

As the compounds represented by the formula (5), compounds representedthe following formula (5-3) are still preferable.

In the above formula, R⁵¹³ and R⁵¹⁸ respectively have the same meaningsas those in the formula (5-1) and the preferable ranges thereof are alsothe same. R⁵² represents an alkyl group having from 1 to 20 carbonatoms. In the case where R⁵¹³ and R⁵¹⁸ are both hydrogen atoms, R⁵²preferably represents an alkyl group having from 2 to 12 carbon atoms,more preferably an alkyl group having from 4 to 12 carbon atoms, morepreferably an alkyl group having from 6 to 12 carbon atoms andparticularly preferably an n-octyl group, a tert-octyl group, a2-ethylhexyl group, an n-decyl group or an n-dodecyl group. A2-ethylhexyl group is the most desirable.

In the case where R⁵¹³ and R⁵¹⁸ are both not hydrogen atoms, R⁵²preferably represents an alkyl group having not more than 20 carbonatoms and making the molecular weight of the compound of the formula(5-3) 300 or more.

In the invention, the compounds represented by the formula (5) can besynthesized by a method described in J. Am. Chem. Soc., vol. 63, p. 3452(1941).

Next, specific examples of the compounds represented by the formula (5)will be presented, though the invention is not restricted to thesespecific examples.

In the cellulose acylate film according to the invention, it isdesirable that the spectral transmittance at the wavelength of 380 nm is45% or more but not more than 95% and the spectral transmittance at thewavelength of 350 nm is 10% or less. The spectral transmittance isdetermined in practice by measuring the transmittance at 300 to 450 nmin wavelength of a sample (13 mm×40 mm) at 25° C. and 60% RH by using aspectrophotometer (U-3210, manufactured by HTACHI, Ltd.). Tilt width isdetermined as (wavelength at 72%−wavelength at 5%). Limiting wavelengthis represented by (tilt width/2)+wavelength at 5%. Absorption end isexpressed in the wavelength at the transmittance of 0.4%. Thus, thetransmittances at 380 nm and 350 nm are evaluated.

(Evaluation of Physical Properties of Cellulose Acylate Film) (OpticalPerformance)

(Change in Optical Performance of Film after High-Humidity Treatment)

It is desirable that the film having been treated at 60° C. and 90% RHfor 240 hours shows changes in Re and Rth of not more than 15 nm, morepreferably not more than 12 nm and more preferably not more than 10 nm.

(Change in Optical Performance of Film after High-Temperature Treatment)

Also, it is desirable that the film having been treated at 80° C. for240 hours shows changes in Re and Rth of not more than 15 nm, morepreferably not more than 12 nm and more preferably not more than 10 nm.

It is desirable that the thickness of the cellulose acylate film of theinvention is from 10 to 120 μm, more preferably from 20 to 100 μm andmore preferably from 30 to 90 μm.

(Retardation Change Before and after Stretching Film)

It is preferable that the in-plane retardations of the cellulose acylatefilm of the invention before and after stretching fulfills the followingnumerical formula (5).

|Re(n)−Re(0)|/n≦1.0.  Numerical formula (5)

In the above formula, Re(n) means the in-plane retardation (nm) of thefilm having been stretched by n (%), while Re(0) means the in-planeretardation (nm) of the unstretched film.

The above-described evaluation was conducted by preparing a sample (100mm×100 mm) and stretching it in the machine direction (MD) or in thetransverse direction (TD) with the use of a fixed uniaxial stretchingmachine at a temperature of 140° C. The in-plane retardation Re of eachsample is measured before and after the stretching with the use of anautomatic birefringence analyzer “KOBRA-21ADI”.

<Usage of Cellulose Acylate Film> (Optically Compensatory Film)

The cellulose acylate film of the invention is usable for variouspurposes. It is particularly effective to employ the cellulose acylatefilm of the invention as an optically compensatory film in a liquidcrystal display. An optically compensatory film means an opticalmaterial which is usually employed in liquid crystal displays tocompensate for phase contrast. Namely, it has the same meaning as aphase contrast plate, an optically compensatory sheet, etc. Because ofhaving birefringent properties, an optically compensatory film isemployed in order to relieve coloration in a display screen of a liquidcrystal display or improve viewing angle characteristics.

It is preferable that the cellulose acylate film of the invention hassmall optical anisotropy (i.e., 0≦Re≦10 and |Rth|≦25 concerning Re andRth) and small wavelength dispersion (i.e., |Re₍₄₀₀)−Re₍₇₀₀)|≦10 and|Rth₍₄₀₀₎−Rth₍₇₀₀₎|≦35). When it is used together with an opticallyanisotropic layer having birefringence, therefore, the opticalperformance of the optically anisotropic layer can be exclusivelyachieved without showing any undesired anisotropy. In the case of usingthe cellulose acylate film of the invention as an optically compensatoryfilm in a liquid crystal display, it is therefore favorable that theoptically anisotropic layer used together has Re₆₃₀ of from 0 to 200 nmand |Rth₆₃₀| of form 0 to 400 nm. Any optically anisotropic layer may beused so long as its Re₆₃₀ and Rth₆₃₀ fall within the respective rangesas defined above.

In the liquid crystal display having the cellulose acylate film of theinvention, any optically anisotropic layer required in the opticallycompensatory film can be employed without particularly restricted by theoptical performance of the liquid crystal cell or the driving system.The optically anisotropic layer employed together may be made of eithera composition containing a liquid crystal compound or a birefringentpolymer film. It is also possible to combinedly use these opticallyanisotropic layers.

(Optically Anisotropic Layer Containing Liquid Crystal Compound)

In the case of using an optically anisotropic layer containing a liquidcompound as the optically anisotropic layer, a discotic liquid crystalcompound or a rod-shaped liquid crystal compound is preferred.

(Discotic Liquid Crystal Compound)

Examples of the discotic liquid crystal compound usable in the inventioninclude compounds described in various documents [C. Destrade et al.,Mol. Crysr. Liq. Cryst., vol. 71, p. 111 (1981); ed. by NihonKagalcu-kai, Kikan Kagaku Sosetsu, No. 22, Ekisho no Kagaku, chap, 5,chap. 10, par. 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. Comm.,page 1794 (1985); and J. Zhang et al., J. Am. Chem. Soc., vol. 116, page2655 (1994)).

In the optically anisotropic layer, it is preferable that the discoticliquid crystal molecules have been fixed in the orientated state. It ismost desirable that these molecules have been fixed via a polymerizationreaction. Polymerization of discotic liquid crystal molecules isreported in JP-A-8-27284. To fix discotic liquid crystal molecules bypolymerization, it is necessary to attach a polymerizable group as asubstituent to the disc core of a discotic liquid molecule. When such apolymerizable group is attached directly to the disc core, however, thefixed state can be hardly maintained during the polymerization.Therefore, a linking group is introduced between the disc core and thepolymerizable group. Such discotic liquid crystal molecules havingpolymerizable group are disclosed in JP-2001-4387.

(Rod-Shaped Liquid Crystal Compound)

Examples of the rod-shaped liquid crystal compound usable in theinvention include azomethines, azoxys, cyanobiphenyls, cyanophenylesters, benzoic acid esters, cyclohexanecarboxlic acid phenyl esters,cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines,alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans andalkenylcyclohexylbenzonitriles. In addition to these low-molecularweight liquid crystal compounds, use can be also made of high-molecularweight liquid crystal compounds.

In the optically anisotropic layer, it is preferable that rod-shapedliquid crystal molecules are fixed in the orientated state, mostdesirably having been fixed via a polymerization reaction. Examples ofthe polymerizable rod-shaped liquid crystal compound usable in theinvention include compounds described in Makromol. Chem., vol. 190, p.255 (1989), Advanced Materials, vol. 5, p. 107 (1993), U.S. Pat. No.4,683,327, U.S. Pat. No. 5,622,648, U.S. Pat. No. 5,770,107, WO95/22586, WO 95/24455, WO 97/00600, WO 98/23580, WO 98/52905,JP-A-1-272551, JP-A-6-16616, JP-A-7-110469, JP-A-11-80081 andJP-A-2001-328973.

(Optically Anisotropic Layer Made of Polymer Film)

As described above, the optically anisotropic layer in the invention maybe made of a polymer film. In such a case, the polymer film comprises apolymer capable of exhibiting optical anisotropy. Examples of such apolymer include polyolefins (for example, polyethylene, polypropyleneand polynorbonene polymers), polycarbonate, polyallylate, polysulfone,polyvinyl alcohol, polymethacrylic acid esters, polyacrylic acid esters,cellulose esters (for example, cellulose triacetate and cellulosediacetate), and so on. It is also possible to use a copolymer of thesepolymers or a polymer mixture.

It is preferable that the optical anisotropy of the polymer film isachieved by stretching the polymer film. Uniaxial or biaxial stretchingis preferred. More specifically speaking, it is preferable to employlongitudinal uniaxial stretching with the use of a difference incircumferential speed between two or more rolls, tenter stretching inthe width direction while clipping the polymer film at both sides, orbiaxial stretching by combining the same. It is also possible that twoor more polymer films are stacked so that the optical properties of thecomposite films fulfill the above requirements as a whole. To minimizeirregularities in birefringence, it is preferable to produce the polymerfilm by the solvent cast method. The thickness of the polymer filmpreferably ranges from 20 to 500 μm, most desirably from 40 to 100 μm.

Alternatively, use can be preferably made of a film-forming method whichcomprises using at least one polymer material selected from the groupconsisting of polyamide, polyimide, polyester, polyether ketone,polyamidimde, polyesterimide and polyaryl-ether ketone as a material forforming the optically anisotropic layer, coating a substrate with asolution of the polymer material dissolved in a solvent and drying thesolvent to give a film. In this case, use may be preferably made of atechnique of stretching the polymer film with the substrate to developoptical anisotropy, thereby using as an optically anisotropic layer. Thecellulose acylate film of the invention can be preferably employed asthe substrate in the above case. It is also preferable that such apolymer film is formed on another substrate and then, after strippingthe polymer film from the substrate, laminating it on the celluloseacylate film of the invention and using it as an optically anisotropiclayer. According to this method, the polymer film thickness can bereduced. Namely, the polymer film thickness is preferably 50 μm or less,more preferably from 1 to 20 μm.

(Polarizing Plate)

Next, the usage of the cellulose acylate film of the invention will bedescribed.

The cellulose acylate film of the invention is particularly useful as aprotective film for a polarizing plate. In the case of using thecellulose acylate film of the invention as a protective film for apolarizing plate, the polarizing plate may be constructed by a usuallyemployed method without specific restriction, A common method comprisestreating the obtained cellulose acylate film with an alkali and thenlaminating on both faces of a polarizer, which has been constricted bydipping a polyvinyl alcohol film in an iodine solution and stretched, byusing a completely saponified aqueous polyvinyl alcohol solution. As analternative for the alkali treatment, use may be made of a treatment forfacilitating adhesion as reported in JP-A-6-94915 or JP-A-6-118232.

Examples of the adhesive to be used for laminating the treated face ofthe protective film on the polarizer include polyvinyl alcohol-basedadhesives such as polyvinyl alcohol and polyvinyl butyral, vinyl-basedlatexes such as butyl acrylate and so on.

(Evaluation of Adhesiveness Between Protective Film and Polarizer)

In stacking the treated face of a protective film on a polarizer, asufficient adhesiveness is required. The adhesiveness of the celluloseacylate film of the invention is tested by laminating on the polarizer,sufficiently drying adhesive components and then repeatedly peeling offthe protective film 50 times. Then, the adhesiveness is evaluated in thefollowing three grades: (A) no delamination found after peeling off 50times; (B) delamination found after peeling off from 30 to 50 times; and(C) delamination found after peeling off less than 30 times.

The polarizing plate is composed of the polarizer and the protectivefilms protecting both faces thereof. It further has a protect film onone face of the polarizing plate and a separate film on the oppositeface thereof. The protect film and the separate film are employed inorder to protect the polarizing plate during shipment, productinspection and other steps. In this case, the protect film, which aimsat protecting the surface of the polarizing plate, is stacked on theface opposite to the face to be stacked on a liquid crystal plate. Onthe other hand, the separate film, which aims at covering the adhesivelayer to be boned to the liquid crystal plate, is stacked on the face ofthe polarizing plate to be stacked on the liquid crystal face.

In a liquid crystal display, a substrate containing liquid crystals isusually provided between two polarizing plates. The protective film forpolarizing plate comprising the cellulose acylate film of the inventionenables the achievement of excellent display characteristics at anysite. It is preferable to use the protective film in the liquid crystalcell side as an optically compensatory film together with an opticallyanisotropic layer. It is particularly preferable to use the protectivefilm for polarizing plate as a protective film for polarizing plate asthe outmost layer in the display side of a liquid crystal display, sincea transparent hard coat layer, an antiglare layer, an antireflectivelayer, etc. are formed therein.

(Liquid Crystal Display) (Constitution of Commonly Used Liquid CrystalDisplay)

Next, usage of the cellulose acylate film of the invention as a memberconstituting a liquid crystal display will be described.

As discussed above, the cellulose acylate film of the invention isappropriately usable as a protective film for a polarizing plate. In thecase of using the thus obtained polarizing plate in a liquid crystaldisplay, the liquid crystal display comprises a liquid crystal cellhaving liquid crystals between a pair of electrode substrates and twopolarizing plates, one of which is provided in one-side of the cell andthe other of which is provided in the other side of the cell, preferablytogether with at least one optically compensatory film provided betweenthe liquid crystal cell and the polarizer.

In the case of using the cellulose acylate film as the opticallycompensatory film, the transmission axis of the polarizer and the slowaxis of the cellulose acylate film may be located at an arbitrary angle.A liquid crystal display comprises a liquid crystal cell having liquidcrystals between a pair of electrode substrates, two polarizers providedin both sides of the cell, and at least one optically compensatory filmprovided between the liquid crystal cell and the polarizer.

The liquid crystal layer of the liquid crystal cell is usuallyconstructed by enclosing liquid crystals into a space formed byinserting a spacer between two substrates. A transparent electrode layeris formed as a transparent membrane containing an electricallyconductive substance. The liquid crystal cell may further have a gasbarrier layer, a hard coat layer or an under coat layer (employed forlaminating the transparent electrode layer). These layers are usuallyformed on the substrate. The thickness of the liquid crystal cellsubstrate is generally from 50 μm to 2 mm.

(Liquid Crystal Display Types)

The cellulose acylate film of the invention is usable in liquid crystaldisplays in various display modes. There have been proposed variousdisplay modes, for example, TN (twisted nematic), IPS (in-planeswitching), FLC (ferroelectric liquid crystal), AFLC (anti-ferroelectricliquid crystal), OCB (optically compensatory bend), STN (super twistednematic), VA (vertically aligned), ECB (electrically controlledbirefringence) and HAN (hybrid aligned nematic) modes. There have beenfurther proposed display modes obtained by split orientation of theabove display modes. The cellulose acylate film of the invention iseffective in liquid crystal displays in any of these display modes. Itis also effective in liquid crystal displays of transmission, reflectionand semi-transmission types.

(Liquid Crystal Display of TN Type)

The cellulose acylate film of the invention may be used as the supportof an optically compensatory sheet or a protective film for a polarizingplate in a TN type liquid crystal display having a liquid crystal cellin the TN mode. Liquid crystal cells in the TN mode and liquid crystaldisplays of the TN type have been well known for a long time. Opticallycompensatory sheets to be used in TN type liquid crystal displays aredescribed in JP-A-3-9325, JP-A-6-148429, JP-A-8-50206 and JP-A-9-26572and also reported by Mori, et al., Jpn. J. Appl. Phys., vol. 36 (1997),p. 143 and p. 1068.

(Liquid Crystal Display of STN Type)

The cellulose acylate film of the invention may be used as the supportof an optically compensatory sheet or a protective film for a polarizingplate in an STN type liquid crystal display having a liquid crystal cellin the STN mode. In general, rod-shaped liquid crystal molecules in theliquid crystal cell of a STN type liquid crystal display are twisted by90 to 360° and the product (And) of the refractive anisotropy (Δn) ofthe rod-shaped liquid crystal molecule and the cell gap (d) ranges from300 to 1500 nm. Optically compensatory sheets usable in the STN typeliquid crystal displays are described in JP-A-2000-105316.

(Liquid Crystal Display of VA Type)

The cellulose acylate film of the invention may be used as the supportof an optically compensatory sheet or a protective film for a polarizingplate in a VA type liquid crystal display having a liquid crystal cellin the VA mode. It is preferable to control the Re retardation value andthe Rth retardation value of the optically compensatory sheet to be usedin a VA type liquid crystal display unit respectively to 0 to 150 nm and70 to 400 nm. It is still preferable to control the Re retardation valueto 20 to 70 nm. In the case of using two optically anisotropic polymerfilms in a liquid crystal display unit of the VA type, the Rthretardation values of the films preferably range from 70 to 250 nm. Inthe case of using a single optically anisotropic polymer film in aliquid crystal display unit of the VA type, the Rth retardation value ofthe film preferably ranges from 150 to 400 nm. Use may be also made of aliquid crystal display unit of the VA type in the split orientationsystem as described in, for example, JP-A-10-123576.

(Liquid Crystal Display of IPS Type and Liquid Crystal Display of ECBType)

The cellulose acylate film of the invention may be particularlyadvantageously used as the support of an optically compensatory sheet ora protective film for a polarizing plate in an IPS type liquid crystaldisplay having a liquid crystal cell in the IPS mode or an ECB typeliquid crystal display having a liquid crystal cell of the ECB mode, ora protective film of a polarizing plate therein. In these modes, aliquid crystal material is orientated almost in parallel in blackdisplay. Namely, liquid crystal molecules are orientated in parallelwith the substrate plane under loading no voltage, thereby giving blackdisplay. A polarizing plate having the cellulose acylate film of theinvention contributes to the enlargement in viewing angle and theimprovement in contrast in these modes. In this embodiment, it isfavorable to employ a polarizing plate with the use of a celluloseacylate film having a smaller optical anisotropy as the protective filmlocated between the liquid crystal cell and the polarizing plate (i.e.,the protective film in the cell side) of the polarizing plate-protectivefilms provided above and below the liquid crystal cell, at least in oneside of the liquid crystal cell. It is still favorable in these modes tocontrol the retardation value of the optically anisotropic layerprovided between the protective films of the polarizing plate and theliquid crystal cell to not more than twice of Δn·d.

(Liquid Crystal Display of OCB Type and Liquid Crystal Display of HANType)

The cellulose acylate film of the invention may be also advantageouslyused as the support of an optically compensatory sheet or a protectivefilm for a polarizing plate in an OCB type liquid crystal display havinga liquid crystal cell in the OBC mode or a HAN type liquid crystaldisplay having a liquid crystal cell in the HAN mode. It is preferablethat an optically compensatory sheet to be used in an OCB type liquidcrystal display or a HAN type liquid crystal display has a directiongiving the minimum absolute retardation value neither in the opticallycompensatory sheet plane nor in the normal line direction. The opticalproperties of an optically compensatory sheet to be used in an OCB typeliquid crystal display or a HAN type liquid crystal display aredetermined depending on the optical properties of the opticallyanisotropic layer, the optical properties of the support and theconfiguration of the optically anisotropic layer and the support.Optically compensatory sheets to be used in an OCB type liquid crystaldisplay or a HAN type liquid crystal display are described inJP-A-9-197397 and also reported by Mori, et al., Jpn. J. Appl. Phys.,Vol. 38 (1999), p. 2837.

(Liquid Crystal Display of Reflection Type)

The cellulose acylate film of the invention may be also advantageouslyused as the support of an optically compensatory sheet in reflectiontype liquid crystal displays such as TN type, STN type, —HAN type and GH(guest-host) type. These display modes have been well known for a longtime. Liquid crystal displays of the TN reflection type are described inJP-A-10-123478, WO 9848320 and Japanese Patent No. 3022477, while anoptically compensatory sheet to be used in a reflection type liquidcrystal display is described in WO 00-65384.

(Other Liquid Crystal Displays)

The cellulose acylate film of the invention may be also advantageouslyused as the support of an optically compensatory sheet or a protectivefilm for a polarizing plate in an ASM (axially symmetric alignedmicrocell) type liquid crystal display having a liquid crystal cell inthe ASM mode. A liquid crystal cell of the ASM mode is characterized bybeing held by a resin spacer allowing to control the cell thickness fromsite to site. Other properties thereof are the same as liquid crystalcells in the TN mode. A liquid crystal cell in the ASM mode and an ASMtype liquid crystal display are reported by Kume et al, SID 98 Digest1089 (1998).

(Hard Coat Film, Antiglare Film and Antireflective Film)

Furthermore, the cellulose acylate film of the invention isappropriately usable in a hard coat film, an antiglare film and anantireflective film. In order to improve the visibility of a flat paneldisplay such as LCD, PDP, CRT or EL, any or all of a hard coat layer, anantiglare layer and an antireflective layer may be formed on one or bothfaces of the cellulose acylate film of the invention. Preferredembodiments of these antiglare and antireflective films are described indetail in Japan Institute of Invention and Innovation Journal ofTechnical Disclosure No. 2001-1745 (2001 Mar. 15, Japan Institute ofInvention and Innovation), p. 54 to 57, and the cellulose acylate filmof the invention is appropriately usable therein. It is also possible toform at least any one of a hard coat layer, an antiglare layer and anantireflective layer on the surface of the polarizing plate as describedabove to give a functional polarizing plate. Such functional polarizingplates are appropriately usable in liquid crystal displays.

(Transparent Substrate of Liquid Crystal Cell)

Because of having an optical anisotropy close to zero and a hightransparency, the cellulose acylate film of the invention is usable as asubstrate for a liquid crystal glass substrate (i.e., a transparentsubstrate in which driving liquid crystals are enclosed) in a liquidcrystal display.

Since a transparent substrate in which driving liquid crystals areenclosed should have excellent gas-barrier properties, a gas barrierlayer may be formed on the surface of the cellulose acylate film of theinvention, if necessary. Although the gas barrier layer is notrestricted in form or material, it can be formed by depositing SiO₂ orthe like on at least one face of the cellulose acylate film of theinvention. Alternatively, it is also possible to form a polymer coatlayer having relatively high gas barrier properties, for example, avinylidene chloride polymer of a vinyl alcohol polymer. An appropriatemethod may be selected from them.

In the case of using as a transparent substrate in which driving liquidcrystals are enclosed, a transparent electrode for driving liquidcrystals may be provided. Although the transparent electrode is notparticularly restricted, it may be formed by laminating a metallicmembrane, a metal oxide membrane or the like on at least one face of thecellulose acylate film of the invention. A metal oxide membrane ispreferred from the viewpoints of transparency, electrical conductivityand mechanical characteristics. Among all, a thin membrane made ofindium oxide containing tin oxide as the main component together withfrom 2 to 15% of zinc oxide is preferably employed. These techniques aredisclosed in, for example, JP-A-2001-125079 and JP-A-2000-227603.

(Photographic Film Support)

The cellulose acylate film of the invention is applicable to supports ofsilver halide photographic materials and various material formulationsand processing methods reported in patent documents relating tophotographic sensitive materials are applicable. Regarding thetechniques, JP-A 2000-105445 has detailed descriptions of color negativefilms, and the cellulose acylate film of the invention is favorably usedin these. Also preferably, the film of the invention is applicable tosupports of color reversal silver halide photographic materials, andvarious materials and formulations and methods for processing themdescribed in JP-A 11-282119 are applicable to the invention.

Next, examples of the invention will be provided, though the inventionis not construed as being restricted thereto.

<Production of Cellulose Acetate Film> Example 1-1 Preparation ofCellulose Acetate Solution A (CAL-1)

The composition as will be shown below was fed into a mixing tank andstirred under heating to thereby dissolving individual components, thusgiving a cellulose acetate solution A. As the cellulose acylate, use wasmade of one having an acylation ratio (Ac:OH=2.98:0.02, wherein Acindicates acetyl substituent; OH indicates unsubstituted hydroxyl group;and the ratio means the acylation ratio).

{Composition of Cellulose Acetate Solution A (CAL-1)}

Cellulose acetate (acylation ratio   100 parts by mass (weight) Ac =2.98) Methylene chloride (first solvent) 402.0 parts by mass Methanol(second solvent)  60.0 parts by mass

(Preparation of Mat Agent Solution (ML-1))

20 parts by mass of silica particles having a mean particle size of 16nm (AEROSIL R972 by Nippon Aerosil) and 80 parts by mass of methanolwere well stirred and mixed for 30 minutes to prepare a dispersion ofsilica particles. The dispersion was put into a disperser along with thefollowing composition thereinto, and further stirred therein for atleast 30 minutes to dissolve the components, thereby preparing a matagent solution.

{Composition of Mat Agent Solution}

Dispersion of silica particles 10.0 parts by mass (mean particle size:16 nm) Methylene chloride (first solvent) 76.3 parts by mass Methanol(second solvent)  3.4 parts by mass Cellulose acylate solution (CAL-1)10.3 parts by mass

(Preparation of Additive Solution (AD-1))

The following composition was put into a mixing tank, and heated withstirring to dissolve the components, thereby preparing an additivesolution (AD-1).

{Composition of Additive Solution (AD-1)}

Rth-lowering agent (119) 33.2 parts by mass Wavelength distributionregulator (UV-102)  5.7 parts by mass Methylene chloride (first solvent)58.4 parts by mass Methanol (second solvent)  8.7 parts by massCellulose acylate solution (CAL-1) 12.8 parts by mass

(Production of Cellulose Acylate Film (101))

94.6 parts by mass of the cellulose acylate solution (CAL-1), 1.3 partsby mass of the mat agent solution (ML-1), and 4.1 parts by mass of theadditive solution (AD-1) were separately filtered, and then mixed. Usinga band caster, the mixture was cast on a band. In the above-mentionedcomposition, the ratio by mass of the Rth-lowering agent (119) and thewavelength distribution regulator (UV-102) to cellulose acylate was 6%by mass and 1% by mass, respectively. The film having a remainingsolvent content of 80% by mass was stripped off from the band, and driedat 140° C. for 20 minutes to give a cellulose acylate film (101). Theremaining solvent content of the thus-produced cellulose acylate film(101) was less than 0.1% by mass, and the thickness of the film was 80μm.

Example 1-2 Preparation of Additive Solution (AD-2)

The procedure of preparing the additive solution (AD-1) was followed butusing an Rth-lowering agent (265) as a substitute for the Rth-loweringagent (119) to give an additive solution (AD-2).

(Production of Cellulose Acylate Film (101))

The procedure of preparing the cellulose acylate film (101) was followedbut using the additive solution (AD-2) as a substitute for the additivesolution (AD-1) to give a cellulose acylate film (102). The remainingsolvent content of the thus-produced cellulose acylate film was lessthan 0.1% by mass, and the thickness of the film was 80 μm.

Example 1-3 Production of Cellulose Acylate Film (103)

The procedure of preparing the cellulose acylate film (102) was followedbut stripping off the film having a remaining solvent content of 30% bymass from the band to give a cellulose acylate film (103). The remainingsolvent content of the thus-produced cellose acylate film was less than001% by mass, and the thickness of the film was 80 μm.

Example 1-4 Preparation of Additive Solution (AD-2′)

An additive solution (AD-2′) was prepared as in the preparation of theadditive solution (AD-2) but increasing the amount of the Rth-loweringagent (265).

{Composition of Additive Solution (AD-2′)}

Rth-lowering agent (265) 177.1 parts by mass Wavelength distributionregulator (UV-102)  5.7 parts by mass Methylene chloride (first solvent) 58.4 parts by mass Methanol (second solvent)  8.7 parts by massCellulose acylate solution (CAL-1)  12.8 parts by mass(Production of cellulose acylate film (104))

The procedure of producing the cellulose acylate film (102) was followedbut using the above additive solution (AD-2′) as a substitute for theadditive solution (AD-2). In this composition, the ratio by mass of theRth-lowering agent (265) and the wavelength distribution regulator(UV-102) to cellulose acylate was 32% by mass and 1% by mass,respectively. The film having a remaining solvent content of 80% by masswas stripped off from the band, and dried at 115° C. for 20 minutes togive a cellulose acylate film (104). The remaining solvent content ofthe thus-produced cellulose acylate film (104) was less than 0.1% bymass, and the thickness of the film was 80 μm.

Comparative Example 1-1 Production of Cellulose Acylate Film (1-1)

The procedure of preparing the cellulose acylate film (101) was followedbut not using the additive solution (AD-1) to give a cellulose acylatefilm (1-1). The remaining solvent content of the thus-produced celluloseacylate (1-1) film was less than 0.1% by mass, and the thickness of thefilm was 80 μm.

Comparative Example 1-2 Production of Cellulose Acylate Film (1-2)

The procedure of preparing the cellulose acylate film (104) was followedbut stripping off the film having a remaining solvent content of 30% bymass from the band to give a cellulose acylate film (1-2). The remainingsolvent content of the thus-produced cellulose acylate film (1-2) wasless than 0.1% by mass, and the thickness of the film was 80 μm.

Example 2-1 Preparation of Cellulose Acylate Solution (CAL-2)

The procedure of preparing the cellulose acylate solution (CAL-1) wasfollowed but using cellulose acylate containing propionyl group andhaving an acylation ratio 2.87 (Ac:Pro:OH=2.08:0.79:0.13) as asubstitute for the cellulose acylate having an acylation ratio 2.98(Ac:OH=2.98:0.02) to give a cellulose acylate solution (CAL-2). Proindicates propionyl substituent.

(Preparation of Mat Agent Solution (ML-2))

The procedure of preparing the mat agent solution (ML-1) was followedbut using the cellulose acylate solution (CAL-2) as a substitute for thecellulose acylate solution (CAL-1) to give a mat agent solution (ML-2).

(Preparation of Additive Solution (AD-3))

The procedure of preparing the additive solution (AD-1) was followed butchanging the composition of the additive solution, using the celluloseacylate solution (CAL-2) as a substitute for the cellulose acylatesolution (CAL-1), using ethylphthalyl ethyl glycolate (EPEG) as asubstitute for the Rth-lowering agent (119), adjusting the ratio by massthereof to cellulose acylate to 8% by mass and using no wavelengthdispersion regulator to give an additive solution (AD-3).

(Production of Cellulose Acylate Film (201))

The procedure of preparing the cellulose acylate film (101) was followedbut using the cellulose acylate solution (CAL-2), the mat agent solution(ML-2) and the additive solution (AD-3) respectively as substitutes forthe cellulose acylate solution (CAL-1), the mat agent solution (ML-1)and the additive solution (AD-1) to give a cellulose acylate film (201).The remaining solvent content of the thus-produced cellulose acylatefilm (201) was less than 0.1% by mass, and the thickness of the film was80 μm.

Comparative Example 2-1 Production of Cellulose Acylate Film (2-1)

The procedure of preparing the cellulose acylate film (201) was followedbut not using the additive solution (AD-3) to give a cellulose acylatefilm (2-1). The remaining solvent content of the thus-produced celluloseacylate film (2-1) was less than 0.1% by mass, and the thickness of thefilm was 80 μm.

Table 2 summarizes various physical properties of the cellulose acylatefilm samples of the invention (102) to (104) and the comparative samples(1-1), (1-2) and (2-1) produced above. Thus, it can be understood thateach of the cellulose acylate film samples of the invention fulfillseither the requirement of Tg being lower by 5 to 50° C. or requirementof the half value width of the X-ray diffraction being 110 to 300%,compared with the comparative samples not containing the additive, hasRe and Rth both falling within the desired ranges, and shows improveddimensional change, modulis of elasticity, vapor transmission rate, tearstrength and coefficient of humidity expansion.

TABLE 1 Cellulose acylate film Additive Process conditions Amount ofCellulose acylate Rth-lowering Wavelength solvent Acylation Mat agentdispersion regulator remaining in Drying Sample ratio Solution solutionSolution Amount* Amount* stripping temp. No. Ac Pro No. No. No. Type (%)Type (%) (%) (° C.) Ex. 1-1 101 2.98 — CAL-1 ML-1 AD-1 119 6 UV-102 1 80140 Ex. 1-2 102 2.98 — CAL-1 ML-1 AD-2 265 6 UV-102 1 80 140 Ex. 1-3 1032.98 — CAL-1 ML-1 AD-2 265 6 UV-102 1 30 140 Ex. 1-4 104 2.98 — CAL-1ML-1 AD-2′ 265 32  UV-102 1 80 115 Comparative 1-1 2.98 — CAL-1 ML-1 — —— — — 80 140 Ex. 1-1 Comparative 1-2 2.98 — CAL-1 ML-1 AD-2′ 265 32 UV-102 1 30 115 Ex. 1-2 Ex. 2-1 201 2.08 0.79 CAL-2 ML-2 AD-3 EPEG 8 — —80 140 Comparative 2-1 2.08 0.79 CAL-2 ML-2 — — — — — 80 140 Ex. 2-1Amount*: a ratio by mass to cellulose acylate.

TABLE 2 Physical properties of cellulose acylate film Half valueRetardation Sample Tg width in X-ray Re Rth |Re₄₀₀-Re₇₀₀||Rth₄₀₀-Rthe₇₀₀| No. (° C.) diffraction (nm) (nm) (nm) (nm) Ex. 1-1 101142 1.62 0.02 3.2 2.1 15 Ex. 1-2 102 150 2.06 0.05 1.5 3.5 16 Ex. 1-3103 152 1.25 0.01 1.1 3.2 14 Ex. 1-4 104 114 1.85 0.2 6.5 4.5 15Comparative Ex. 1-1 1-1 190 1.35 3.7 3.7 15 39 Comparative Ex. 1-2 1-2112 1.06 0.7 9.6 5.2 15 Ex. 2-1 201 152 1.73 0.1 22 7.5 25 ComparativeEx. 2-1 2-1 184 0.92 4.2 51 14 38 Physical properties of celluloseacylate film Vapor Coefficient of Dimensional Modulus of transmissionhumidity Sample change elasticity rate (g/m² · Tear strength expansionNo. (%) (kgf/mm²) 24 hrs) (kg cm/cm) (10⁻⁶/% RH) Ex. 1-1 101 0.08 4271350 18 20 Ex. 1-2 102 0.06 452 1420 22 24 Ex. 1-3 103 0.10 442 1350 1921 Ex. 1-4 104 0.14 416 1260 14 18 Comparative Ex. 1-1 1-1 0.16 389 220031 52 Comparative Ex. 1-2 1-2 0.18 408 1230 12 18 Ex. 2-1 201 0.11 3891750 15 32 Comparative Ex. 2-1 2-1 0.21 365 2350 29 45

<Construction of Polarizing Plate>

The cellulose acylate films of the invention were employed as protectivefilms for polarizing plate and evaluated in performance.

Examples 11-1 to 11-4 and 12-1 and Comparative Examples 11-1 to 11-2 and12-1 Alkali Saponification

The cellulose acylate film sample (101) of the invention was dipped inan aqueous 1.5 mol/L sodium hydroxide solution at 55° C. for 2 minutes.Then, it was washed in a wash water bath at room temperature, andneutralized with 0.05 mol/L sulfuric acid at 30° C. Again, it was washedin a wash water bath at room temperature, and dried with a hot airstream at 100° C. The contact angle on the surface of the thussaponified cellulose acylate film sample was measured.

Similarly, the samples (102) to (104) and (201) of the invention and thecomparative samples (1-1) to (1-2) and (2-1) were subjected to thealkali saponification and the contact angles were measured.

(Construction of Polarizer)

A rolled polyvinyl alcohol film having a thickness of 80 μm wascontinuously stretched 5-fold in an aqueous iodine solution, and driedto prepare a polarizer of 20 μm in thickness.

(Construction of Polarizing Plate)

By using an aqueous 3% by mass solution of polyvinyl alcohol “PVA-117H”(manufactured by KURARAY) as an adhesive, to sheets of the celluloseacylate film sample 101 of the invention were stacked while inserting apolarizer between them to give a polarizing plate (P1-1) protected onboth faces with the film samples (101). The saponified face of each filmsample (101) was provided in the polarizer side and the slow axis of thefilm sample (101) was located in parallel to the transmission axis ofthe polarizer. This polarizing plate (P1-1) sustained a sufficientstacking adhesiveness among the two saponified film samples (101) andthe polarizers and a sufficient degree of polarization.

The above procedure was followed to thereby give polarizing plates withthe use of the invention samples (102) to (104) and (201) and thecomparative samples (1-1) to (1-2) and (2-1). The obtained polarizingplates were referred to as polarizing plates (P1-2) to (P1-4) and (P2-1)and polarizing plates (PR1-1) to (PR1-2) and (PR2-1) respectively.

Table 3 summarizes the contact angles after the saponification and thestacking adhesivenesses of the polarizing plates having the celluloseacylate film samples of the invention (P1-1) to (P1-4) and (P2-1) andthe polarizing plates having the comparative samples (PR1-1) to (PR1-2)and (PR2-1). These data indicate that each of the cellulose acylate filmfilms of the invention showed a smaller contact angle after thesaponification, namely, having hydrophilic surface and thus beingimproved in stacking adhesiveness, compared with the comparative samplesnot containing the additive.

TABLE 3 Cellulose acylate film Additive Cellulose Wavelength acylateRth-lowering dispersion Contact angle Acylation agent regulator afterPolarizing plate Sample ratio Amount* Amount* saponification SampleStacking No. Ac Pro Type (%) Type (%) (°) No. adhesiveness Ex. 11-1 1012.98 — 119 6 UV-102 1 24 P1-1 A Ex. 11-2 102 2.98 — 265 6 UV-102 1 24P1-2 A Ex. 11-3 103 2.98 — 265 6 UV-102 1 25 P1-3 A Ex. 11-4 104 2.98 —265 32  UV-102 1 39 P1-4 B Comparative Ex. 1-1 2.98 — — — — — 40 PR1-1 C11-1 Comparative Ex. 1-2 2.98 — 265 32  UV-102 1 39 PR1-2 B 11-2 Ex.12-1 201 2.08 0.79 EPEG 8 — — 27 P2-1 A Comparative Ex. 2-1 2.08 0.79 —— — — 39 PR2-1 C 12-1 Amount*: a ratio by mass to cellulose acylate.

(Method of Evaluating Adhesiveness)

Each protective film was peeled off repeatedly and the adhesiveness wasevaluated as follows: (A) no delamination found after peeling off 50times or more; (B) delamination found after peeling off from 30 to 50times; and (C) delamination found after peeling off less than 30 times.

<Liquid Crystal Display> (Evaluation of Cellulose Acylate Film Mountedto Liquid Crystal Display)

The cellulose acylate films of the invention were employed asconstituting members and amounted to liquid crystal displays followed byevaluation in the following manner. These embodiments are examples ofeffective modes for using the cellulose acylate films of the inventionand it should be understood that the invention is not restrictedthereto.

Example 21 and Comparative Example 21 IPS Mode Liquid Crystal Display

An IPS mode liquid crystal display having the constitution of FIG. 1 wasconstructed.

More specifically speaking, a liquid crystal cell having liquid crystalcompound molecules 17 enclosed between a pair of substrates 16 and 18was located between a pair of polarizers 11 a and 11 b. Then a celluloseacylate film 19 of the invention was provided between the liquid crystalcell and the polarizer in the bottom side 11 b, while a first opticallycompensatory film 15 and a second optically compensatory film 13 wereprovided between the liquid crystal cell and the polarizer in the topside 11 a. The relationships among transmission axes 12 a and 12 b ofthe polarizers and the slow axis of the first optically compensatoryfilm were as mentioned in each example. Although individual constitutingmembers are shown in FIG. 1 as being independent for convenient sake,each member may be integrated together with another member and then putinto the device in some cases (for example, the cellulose acylate film19 may be integrated as a protective film with the polarizer 11 b).

Next, methods of constructing these members will be described in detail

(Construction of IPS Mode Liquid Crystal Cell)

Electrodes were formed on a glass substrate to give intervals betweenadjacent electrodes of 20 μm and a polyimide film was provided thereonas an orientation film, followed by rubbing. A polyimide film wasprovided on one surface of another glass substrate and rubbed to give anorientation film. These two glass plates were piled up and stacked insuch a manner that the orientation films faced to each other, thedistance (gap: d) between the substrates was adjusted to 3.9 μm and therubbing directions of the two glass substrates were in parallel. Next, anematic liquid crystal composition having a refractive index anisotropy(Δn) of 0.0769 and a positive dielectric anisotropy (Δ∈) of 4.5 wasenclosed therein. The dΔn value of the liquid crystal layer was 300 nm.

(Construction of Cellulose Acylate Film 19 and Bottom Side PolarizingPlate 21 b)

In this Example, the cellulose acylate film 19 and the polarizer in thebottom side 11 b were employed in an integrated manner as a bottom sidepolarizing plate 21 b (not shown in the FIGURE). Namely, the polarizingplate (P1-1) constructed by sandwiching the lower polarizer 11 b betweentwo cellulose acylate film sample sheets (101) of Example 1 or thepolarizing plate (PR1-1) constructed in the same manner using thecomparative sample (1-1) was employed as the bottom side polarizingplate 21 b.

(Construction of Second Optically Compensatory film 13)

Fujitak TD80UF (manufactured by FUJI PHOTOFILM Co., Ltd.) waslongitudinally uniaxially 15%-stretched at 150° C. to give an opticallycompensatory film 13 (optical characteristics: Re=5 nm, Rth=70 nm).

(Construction of First Optically Compensatory Film 15) (Formation ofOrientation Film)

After saponifying the surface of the second optically compensatory filmconstructed above, a coating solution for orientation film having thefollowing composition was applied to the film with a wire bar coater ata ratio of 20 μL/m². Then, it was dried under a hot air stream at 60° C.for 60 seconds and subsequently a hot air stream at 100° C. for 120seconds to thereby form a film. The film thus formed was rubbed in adirection parallel to the slow axis of the film to thereby give anorientation film.

(Composition of Coating Solution for Orientation Film)

Denatured polyvinyl alcohol having the  10 parts by mass followingcomposition Water 371 parts by mass Methanol 119 parts by massGlutaraldehyde  0.5 part by mass Tetetramethylammonium fluoride  0.3part by mass

Denatured Polyvinyl Alcohol

(Formation of Optically Anisotropic Layer)

On the thus oriented film, a solution prepared by dissolving 1.8 g ofthe following discotic liquid crystal compound, 0.2 g of ethyleneoxide-denatured trimethylolpropane triacrylate (V#360, manufactured byOSAKA ORGANIC CHEMICAL INDUSTRIES), 0.06 g of a photopolymerizationinitiator (Irgacure 907, manufactured by Ciba-Geigy), 0.02 g of asensitizer (Kayacure DETX, manufactured by NIPPON KAYAKU Co., Ltd.) and0.01 g of the following perpendicular orientation agent in theatmosphere-interface side in 3.9 g of methyl ethyl ketone was coatedwith a #5 wire bar. The obtained product was stacked on a metallic frameand heated in a thermostat at 125° C. for 3 minutes to thereby orientatethe discotic liquid crystal compound, Subsequently, it was UV-irradiatedat 100° C. with the use of a high-pressure mercury lamp at 120 W/cm for30 seconds to thereby crosslink the discotic liquid crystal compound andthen cooled to room temperature by allowing to stand to thereby form anoptically anisotropic layer. Thus, a phase contrast film having thefirst optically compensatory film formed on the second opticallycompensatory film was constructed.

Fluorinated Polymer (Perpendicular Orientation Agent in theAtmosphere-Interface Side)

The optical characteristics of the discotic liquid crystal opticallyanisotropic layer (the first optically compensatory film) alone werecalculated by measuring the incident light angle dependency of Re of thephase contrast film constructed above and subtracting the predeterminedcontribution of the second optically compensatory film therefrom. As aresult, R_(e) was 100 nm, Rth was −55 nm and the average incline angleof liquid crystals was 89.9°. Thus, it was confirmed that the discoticliquid crystals were oriented perpendicularly to the film face. The slowaxis direction was parallel with the rubbing direction.

(Construction of Top Side Polarizing Plate 21 a)

The stretched polyvinyl alcohol film was allowed to absorb iodine togive the top side polarizer 11 a. On one surface of this polarizer, acellulose acetate film “FUJITACK TD80UF” (manufactured by FUJI PHOTOFILMCo., Ltd.) was stacked, on the other surface of the polarizer 11 a, thephase contrast film was stacked in such a manner that the secondoptically compensatory film 13 was located in the polarizer 11 a side,thereby constructing an integrated top side polarizing plate 21 a (notshown in the FIGURE) integrated together with the optically anisotropiclayer.

(Construction of Liquid Crystal Display)

The top side polarizing plate 21 a as described above was stacked on anIPS mode cell in such a manner that the first optically compensatoryfilm side was provided in the liquid crystal cell side. The two slowaxes of the IPS mode cell liquid crystal layer were located in parallelwith the transmission axis 12 a of the polarizer 11 a. Next, the bottomside polarizing plate 21 b constructed above was stacked in such amanner that the transmission axis 12 b of the bottom side polarizer 11 bwas orthogonal to the transmission axis 12 a of the top side polarizer11 a, thereby constructing a liquid crystal display.

(Measurement of Light Leakage from the Liquid Crystal Display ThusConstructed)

In the liquid crystal displays thus constructed, light leakage in blackdisplay observed from an angle of 60° in the left face direction wasmeasured. In the case of using each of the cellulose acylate films ofthe invention, light leakage was extremely compared with the devicesusing the comparative samples. Thus, it can be understood that thecellulose acylate films of the invention are excellent in contrast(i.e., showing little light leakage) and viewing angle characteristicsin color display, when employed in liquid crystal displays.

<Construction of Optically Compensatory Film> Example 31

By using the cellulose acylate film sample (101) of the invention, anoptically compensatory film sample was constructed in accordance withthe method of Example 1 in JP-A-2003-315541.

(Formation of Optically Anisotropic Layer)

A polyimide having a mass-average molecular weight (Mw) of 70,000 and Δnof about 0.04, which had been synthesized from2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride with2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB), was dissolved incyclohexanone to give a 25% by mass solution. This solution was appliedto the cellulose acylate film sample (101) (thickness: 80 μm) preparedin Example 1-1. After heating to 100° C. for 10 minutes, it waslongitudinally uniaxially 15%-stretched at 160° C. to give an opticallycompensatory film in which a polyimide film of 6 μm in thickness wasformed as the optically anisotropic layer on the cellulose acylate filmsample (101) of the invention.

The optical characteristics of this optically compensatory film were asfollows: Re=72 nm, Rth=220 nm, shift angle in orientation axis≦+0.3°.

Comparative Example 31

The procedure of Example 31 was followed but using the comparativesample (1-1) (thickness: 80 μm) as a substitute for the celluloseacylate film sample (101) of the invention to thereby give an opticallycompensatory film in which a polyimide film of 6 μm in thickness wasformed as the optically anisotropic layer on the comparative celluloseacylate film sample (1-1). The optical characteristics of this opticallycompensatory film were as follows: Re=75 nm, Rth=257 nm.

(Evaluation of Mounting on VA Type Liquid Crystal Display)

The optically compensatory films obtained in Example 31 and ComparativeExample 31 were each alkali saponified in the face having no polyimidefilm stacked thereon. Then it was stacked directly on a polarizer withthe use of a polyvinyl alcohol-based adhesive. The stacking wasconducted so that the slow axis direction of the optically compensatoryfilm was orthogonal to the absorption axis of the polarizer. Next, theoptically compensatory film was stacked on a VA liquid crystal panelwith a pressure-sensitive adhesive so that the optically compensatoryfilm was located in the liquid crystal side. In the opposite side of theliquid crystal, a polarizing plate alone was stacked on the VA liquidcrystal panel via a pressure-sensitive adhesive so that the absorptionaxes of the polarizing plates were orthogonal to each other.

The viewing angle characteristics of the liquid crystal displays thusobtained were measured. The polar angle, at which the contrast ratio ofblack display to white display in the 45° direction attains 20 or less(the polar angle of a perpendicular line to the panel being referred toas 0° C. and the polar angle increasing with an increase in diagonalangle), was determined. The case of the optically compensatory filmobtained by using the cellulose acylate film sample (101) of theinvention sustained excellent viewing angle characteristics (i.e.,contrast 20 or higher) up to the polar angle 80°, while the cocoobtained by using the comparative sample (1-1) showed poor viewing angleproperties (ice., polar angle 30°). Thus, it was clarified that thecellulose acylate film of the invention was highly usable as a phasecontrast film for VA mode.

Table 4 summarizes the results of Example 21 and Comparative Example 21and Example 31 and Comparative Example 31.

Compared with the comparative sample (1-1) not containing the additives,the cellulose acylate film sample (101) of the invention has small Re,Small Rth, narrow wavelength dispersion of Re and narrow wavelengthdispersion of Rth. Owing to these characteristics, the cellulose acylatefilm of the invention is effective in lessening color change from anangle and relieving light leakage in black display when employed in IPSmode liquid crystal displays. It is also found out that the celluloseacylate film of the invention can improve the contrast viewing anglecharacteristics when employed in VA mode liquid crystal displays.

TABLE 4 Liquid display device Cellulose acylate film IPS mode AdditiveLight VA mode Rth- Wavelength Optical characteristics leakage ContrastSample lowering dispersion Re Rth |Re₄₀₀-Re₇₀₀| |Rth₄₀₀-Rth₇₀₀| fromviewing angle No. agent regulator (nm) (nm) (nm) (nm) anglecharacteristics Ex. 1-1 101 119 UV-102 0.02 3.2 2.1 15 Ex. 21 No Ex. 3178° Comparative 1-1 — — 3.7 37 15 39 Comparative Yes Comparative 29° Ex.1-1 Ex. 21 Ex. 31

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the described embodiments ofthe invention without departing from the spirit or scope of theinvention. Thus, it is intended that the invention cover allmodifications and variations of this invention consistent with the scopeof the appended claims and their equivalents.

The present application claims foreign priority based on Japanese PatentApplication No. JP2005-111171 filed Apr. 7, 2005, the contents of whichare incorporated herein by reference.

1. A cellulose acylate film comprising an additive, the celluloseacylate film fulfilling at least one of requirements (1) and (2): (1)the cellulose acylate film has a glass transition temperature lower by 5to 50° C. than that of a cellulose acylate film not containing theadditive; and (2) the cellulose acylate film having been heated at 200°C. for 3 hours has a half value width of a diffraction peak at 20 of 10to 15° in an X-ray diffraction pattern thereof, the half value widthbeing 110 to 300% of a half value width of a cellulose acylate film notcontaining the additive and having been heated at 200° C. for 3 hours,and the cellulose acylate film further fulfilling numerical formulae (1)and (2):0≦Re ₆₃₀≦10, and |Rth ₆₃₀|≦25  Numerical formulae (1)|Re ₄₀₀ −Re ₇₀₀|≦10, and |Rth ₄₀₀ −Rth ₇₀₀|≦35  Numerical formulae (2)wherein Re(λ) indicates an in-plane retardation by nm of the celluloseacylate film at a wavelength of λ nm; and Rth(λ) indicates athickness-direction retardation by nm of the cellulose acylate film at awavelength of λ nm.
 2. The cellulose acylate film according to claim 1,which has an absolute value of dimensional change after standing at 60°C. and 90% for 24 hours, the absolute value being 5 to 90% with respectto an absolute value of dimensional change of a cellulose acylate filmnot containing the additive.
 3. The cellulose acylate film according toclaim 1, which has a modulus of elasticity of 101 to 150% with respectto a modulus of elasticity of a cellulose acylate film not containingthe additive.
 4. The cellulose acylate film according to claim 1, whichhas a vapor transmission rate of 30 to 90% with respect to a vaportransmission rate of a cellulose acylate film not containing theadditive.
 5. The cellulose acylate film according to claim 1, which hasa contact angle after alkali saponification of 95% or less with respectto a contact angle after alkali saponification of a cellulose acylatefilm not containing the additive.
 6. The cellulose acylate filmaccording to claim 1, which has a tear strength of 95% or less withrespect to a tear strength of a cellulose acylate film not containingthe additive.
 7. The cellulose acylate film according to claim 1, whichhas a coefficient of humidity expansion of 95% or less with respect to acoefficient of humidity expansion of a cellulose acylate film notcontaining the additive.
 8. The cellulose acylate film according toclaim 1, which is obtained from a starting polymer having an acylationratio of 2.85 to 3.00.
 9. The cellulose acylate film according to claim1, wherein the additive is a compound capable of lowering Rth_(λ) insuch a range as fulfilling numerical formulae (3) and (4):(Rth _(λA) −Rth _(λ0))/A≦<−1.0  Numerical formula (3)0.01≦A≦30  Numerical formula (4) wherein Rth_(λA) indicates Rth_(λ) bynm of a cellulose acylate film containing A % by mass of the compoundcapable of lowering Rth_(λ); Rth₀ indicates Rth_(λ) by nm of a celluloseacylate film not containing the compound capable of lowering Rth_(λ);and A indicates an amount by mass % of the compound capable of loweringRth_(λ) referring a mass of a starting polymer of the cellulose acylatefilm as to
 100. 10. The cellulose acylate film according to claim 1,which the additive is a compound capable of lowering |Re₄₀₀−Re₇₀₀| and|Rth₄₀₀−Rth₇₀₀| in an amount of 0.01 to 30% by mass based on a solidcontent of a starting polymer of the cellulose acylate film.
 11. Thecellulose acylate film according to claim 1, which has a film thicknessof 10 to 120 μm.
 12. A method of producing a cellulose acylate filmaccording to claim 1, which comprises: casting a cellulose acylatesolution containing a solvent on a support to provide a film, strippingoff the film from the support; and drying the film, wherein the film inthe stripping has an amount of the solvent of 50 to 200%.
 13. A methodof producing a cellulose acylate film according to claim 1, whichcomprises: casting a cellulose acylate solution containing a solvent ona support to provide a film, stripping off the film from the support;and drying the film at a temperature of 120 to 160° C.
 14. An opticallycompensatory film comprising: a cellulose acylate film according toclaim 1; and an optically anisotropic layer having Re₆₃₀ of 0 to 200 nmand |Rth₆₃₀| of 0 to 400 nm.
 15. A polarizing plate comprising: apolarizer; and a protective film of a cellulose acylate film accordingto claim
 1. 16. A liquid crystal display comprising a cellulose acylatefilm according to claim 1.